Biology subjects

Forstmeier, W.

Publications and source records attributed to Forstmeier, W..

17 recordsLinked to original sources

bioRxiv2026

Global patterns and evolution of avian song complexity

Why birds evolved complex songs has been a long-standing puzzle. Here, by quantifying song complexity in 4,940 species (83% of all passerines), we show a latitudinal gradient in song complexity, with the most complex songs occurring in temperate, open-habitat bird assemblages characterized by relatively inconspicuous plumage. Using comparative analyses controlled for common ancestry, we find little support for traditional explanations based on sexual selection intensity, intelligence signaling, or species richness. Instead, complex songs evolve primarily in song-learning passerines, especially migrants, habitat generalists, and species breeding in open habitats where structured acoustic signals transmit more efficiently. Together, our findings indicate that global variation in song complexity emerges from the interaction between vocal learning, ecological context, and evolutionary history rather than from a single selective driver.

evolutionary biology↗

bioRxiv2025

The germline-restricted chromosome orchestrates germ cell development in passerine birds

While the definition of germ cell fate has been extensively studied in model organisms, evolutionary innovations and mechanistic novelties may remain hidden in understudied systems. The phenomenon of programmed DNA elimination allows germ cells to acquire germline-restricted genes, offering a novel paradigm of germ cell specificity. In passerine birds, the germline-restricted chromosome (GRC) is eliminated from somatic cells in early embryogenesis, yet the role and consequences of its maintenance in the germ cells remain poorly understood. Here, using the zebra finch Taeniopygia guttata as a model, we combined RNA-seq and Spatial Transcriptomics to construct a high-resolution spatiotemporal expression map to understand the role of the GRC across germ cell development. We found a GRC-linked integrin-BMP signaling in maturing oocytes and tfebGRC upregulation at blastoderm embryos, suggesting the involvement of the GRC in oocyte maturation and germ cell determination. We also identified developmental specialization of GRC-linked gene expression relative to their paralogs on the autosomes and sex chromosomes, revealing a gene repertoire which promotes germline stemness and germline/soma distinction. Together, the passerine GRC constitutes a unique system that manifests germ cell complexity, whilst allowing pinpointing the effects on gene expression that may elucidate vertebrate germ cell fate.

developmental biology↗

bioRxiv2025

Are our 95% CIs only worth 45% confidence?

O_LIWhen multiple studies on the same research question, or multiple analyses of the same dataset are summarized in a meta-analysis, our confidence intervals (CIs) are put to a relentless test of reliability. While we might hope that 95% of the CIs would contain the meta-analytic mean value (and therefore presumably also the true value), a recent meta-analysis of 512 meta-analyses in ecology and evolution suggests that only a sobering 45% of them do. C_LIO_LIAs this paradox of overconfidence continues to confuse researchers, we attempt to explain where most of the heterogeneity in findings might be coming from. Much of it is unsurprising, because conventional 95% CIs reflect only sampling noise and ignore other sources of error such as arbitrary analysis decisions ("model uncertainty"). Being aware of multiple sources of error beyond sampling noise, the replication crisis logically follows from an anticonservative statistical practice that allows for overinterpretation beyond the legitimate inference space, which in fact is narrower than commonly acknowledged. C_LIO_LIWe explain how to calculate extended confidence intervals (CIext) that also cover other sources of biological and analytical heterogeneity, and we clarify which CIext is valid for which extended inference space. We further show how multiple versions of analysis of the same dataset can be merged into a many-analyses meta-analysis (MAMA) which yields a CI that accounts for two sources of error. C_LIO_LIAt the same time, we recognize that high heterogeneity estimates can be artefactual, arising from "comparing apples and oranges" (either in terms of statistical metric or biological interpretation). The estimate of only 45% deserved confidence therefore appears far too pessimistic. Overall, we argue for greater caution in interpreting both confidence intervals and heterogeneity estimates, and for clearer separation of comparable from non-comparable evidence. C_LI

ecology↗

bioRxiv2025

Programmed DNA elimination drives rapid genomic innovation in two thirds of all bird species

Bird genomes are among the most stable in terms of synteny and gene content across vertebrates. However, germline-restricted chromosomes (GRCs) represent a striking exception where programmed DNA elimination confines large-scale genomic changes to the germline. GRCs are known to occur in songbirds (oscines), but have been studied only in a few species of Passerides such as the zebra finch, the key model for passerine genomics. Their presence and evolutionary dynamics in most major passerine lineages remain largely unexplored, with suboscines entirely unexamined by cytogenetic or genomic methods. Here, we present the most comprehensive comparative analysis of GRCs to date, spanning 44 million years of passerine evolution. By generating the first germline reference genomes of an oscine and a suboscine, 22 novel germline draft genomes spanning nearly all major passerine lineages and a germline draft genome of a parrot outgroup, we show that the GRC is likely present in 6,700 passerine species. Our results reveal that the GRC evolves rapidly and distinctly from the standard A chromosomes (autosomes and sex chromosomes), yet retains functionally important, selectively maintained genes. We observed gene and repeat turnover occuring orders of magnitude faster than on the A chromosomes. Some GRC genes, such as cpeb1 and pim1, are widespread from an ancient duplication. In contrast, other GRC genes, like mfsd2b and bmp15, have been independently duplicated onto the GRC multiple times, suggesting adaptive constraints. The discovery of zglp1 on the zebra finch GRC, initially copied from chromosome 30 and subsequently lost from it, indicates functional replacement, where the GRC permits gene loss from the standard genome. As the GRC harbors the only zglp1 copy in most of the [~]4000 Passerides species, GRC loss would compromise essential germline functions. Our findings establish the GRC as a genomic innovator driving rapid germline evolution. This fact highlights its evolutionary significance for passerine diversification and suggests that programmed DNA elimination may be an overlooked yet phylogenetically widespread mechanism in many understudied animal lineages.

genomics↗

bioRxiv2024

Sex and morph variation in activity from early ontogeny to maturity in ruffs (Calidris pugnax)

Intraspecific variation provides the substrate for the evolution of organisms. Ruffs show exceptional phenotypic variation in physiology, appearance and behaviour linked to variation between sexes and male alternative reproductive tactics (ARTs). The male ARTs are associated with the evolution of separate morphs, which are encoded by an autosomal supergene. However, the effects of the supergene on females and chicks are much less well understood. In particular, it is still unknown, whether females also show morph-specific behavioural variation, when behavioural differences emerge during ontogeny, and whether behavioural differences can be detected outside of the breeding context. To address these knowledge gaps, we repeatedly measured the activity in an unfamiliar environment, also known as exploration behaviour, of 109 hand-raised young ruffs throughout their first two years of life. We used automated tracking in an open field arena, and quantified the distance moved within 10 minutes to examine behavioural differences between sexes, morphs and individuals. The activity of young ruffs rapidly increased during the first month after their crouching reflex, a response to potential threats, subsided. Repeatability of individual activity was initially low but increased throughout juvenile ontogeny and was high (R = 0.5) from day 21 onwards. Variation in activity was clearly sex-linked with females moving more than males, indicating potential energetic trade-offs accompanying the strong sexual size dimorphism. In contrast, morph differences in activity remained inconsistent and elusive, both in females and in males. Our results indicate that in species where much of the known behavioural variation is linked to mating tactics, a non-reproductive behaviour can show between-individual variation and clear sex differences, whereas morph differences appear less pronounced.

animal behavior and cognition↗

bioRxiv2023

Sperm traits of the three genetic morphs in the ruff sandpiper

BackgroundThe ruff sandpiper Calidris pugnax is a Palearctic lekking shorebird with three genetic morphs determined by an autosomal inversion. Male morphs differ strikingly in body size, ornaments, endocrinology and mating behavior. Aggressive Independents represent the ancestral haplotype, while female-mimicking Faeders and semi-cooperative Satellites are the inverted haplotypes. Because one inversion breakpoint is homozygous lethal, the inverted haplotypes cannot recombine and are expected to accumulate deleterious mutations. The inversion regions also harbor genes involved in spermatogenesis. However, it remains unknown whether the genetic differences between the morphs also translate into differences in sperm traits. Here, we use a captive-bred population of ruffs to compare sperm swimming speed and morphology among the morphs. ResultsRuff sperm morphologically resembled those of passerines, but moved differently, vibrating from side to side while slowly moving forward, rather than rotating while moving forward. Faeder sperm moved the slowest, which is consistent with the prediction of genetic deterioration over time. However, against expectation, sperm of Independents did not seem to be of the highest quality, i.e., their sperm were not the fastest nor the least variable, and they had sperm with the shortest tail and midpiece. Although the midpiece contains the energy-producing mitochondria, sperm midpiece length was not associated with sperm swimming speed. Instead, two of three velocity metrics weakly positively correlated with head length (absolute and relative). ConclusionsThe three genetically determined ruff morphs showed subtle differences in swimming speed and in the length of some sperm components. However, the between-morph differences in sperm swimming speed were not linked to the differences in morphology. We conclude that there is at best limited evidence for lower-quality sperm in the morphs that carry the inversion, and suggest that the potential for the evolution of morph-specific sperm adaptations may be limited in this system. Lay SummaryThe ruff sandpiper is a shorebird that exhibits three genetically distinct types of males, which differ markedly in body size, ornaments, hormones, and mating behavior. Aggressive Independents represent the type that evolved first. Semi-cooperative Satellites and female-mimicking Faeders evolved later through a specific type of genetic rearrangement called an inversion, in which a segment of a chromosome reversed in orientation. Due to the nature of this inversion, Satellite and Faeder chromosomes are expected to deteriorate over time. However, it remains unclear whether the genetic differences between these morphs, which affect physiological and behavioral traits, also translate into differences in sperm traits. We used a captive population of ruffs to compare sperm swimming speed and length measurements between the three types of males. Faeder sperm was the slowest, which is consistent with expectations based on genetic deterioration over time. However, against our expectations, the sperm of Independents does not appear to have better performance characteristics. Although the midpiece of a sperm is responsible for energy production, the length of the midpiece did not relate to sperm swimming speed.

evolutionary biology↗

bioRxiv2021

Fitness costs of female choosiness in a socially monogamous songbird

Female mate choice is thought to be responsible for the evolution of many extravagant male ornaments and displays, but the costs of being too selective may hinder the evolution of choosiness. Selection against choosiness should be strongest in socially monogamous mating systems, because females may end up without a partner and forego reproduction, especially when many females prefer the same few partners (frequency-dependent selection). Here we quantify the fitness costs of having mating preferences that are difficult to satisfy. We capitalise on the recent discovery that female zebra finches (Taeniopygia guttata) prefer males of familiar song dialect. We measured female fitness in captive breeding colonies in which one third of females were given ample opportunity to choose a mate of their preferred dialect (two thirds of all males; relaxed competition), while two thirds of the females had to compete over a limited pool of mates they preferred (one third of all males; high competition). As expected, social pairings were strongly assortative with regard to song dialect. In the high-competition group, 26% of the females remained unpaired, yet they still obtained relatively high fitness by using brood parasitism as an alternative reproductive tactic. Another 31% of high-competition females paired disassortatively for song dialect. These females showed increased levels of extra-pair paternity, mostly with same-dialect males as sires, suggesting that preferences were not abolished after social pairing. However, females that paired disassortatively for song dialect did not have lower reproductive success. Overall, females in the high-competition group reached equal fitness as those that experienced relaxed competition. Our study suggests that alternative reproductive tactics such as egg dumping can help overcome the frequency-dependent costs of being highly selective in a monogamous mating system, thereby facilitating the evolution of female choosiness.

evolutionary biology↗

bioRxiv2021

Machine learning reveals cryptic dialects that guide mate choice in a songbird

Culturally transmitted communication signals - such as human language or bird song - can change over time through a process of cultural drift, and may consequently enhance the separation of populations, potentially leading to reproductive isolation1-4. Local song dialects have been identified in bird species with relatively simple songs where individuals show high cultural conformity5-10. In contrast, the emergence of cultural dialects has been regarded as unlikely11-13 for species with more variable song, such as the zebra finch (Taeniopygia guttata). Instead, it has been proposed that selection for individual recognition and distinctiveness may lead to a complete spread across the space of acoustic and syntactical possibilities11-15. However, another possibility is that analytical limitations have meant that subtle but possibly salient group differences have not yet been discovered in such species. Here we show that machine learning can distinguish the songs from multiple captive zebra finch populations with remarkable precision, and that these cryptic song dialects drive strong assortative mating in this species. We studied mating patterns across three consecutive generations using captive populations that have evolved in isolation for about 100 generations. Cross-fostering eggs within and between these populations and quantifying social interactions of the resulting offspring later in life revealed that mate choice primarily targets cultural traits that are transmitted during a short developmental time window. Detailed social networks showed that females preferentially approached males whose song resembled that of their adolescent peers. Our study shows that birds can be surprisingly sensitive to cultural traits for mating that have hitherto remained cryptic, even in this well-studied species that is used as a model for song-learning13,14,16-28.

animal behavior and cognition↗

bioRxiv2021

Occasional paternal inheritance of the germline-restricted chromosome in songbirds

All songbirds have one special accessory chromosome1-4, the so-called germline-restricted chromosome (GRC)4-7, which is only present in germline cells and absent from all somatic tissues. Earlier work on the zebra finch (Taeniopygia guttata castanotis) showed that the GRC is inherited only through the female line4,6,8,9 - like mitochondrial DNA7,9-12 - and is eliminated from the sperm during spermatogenesis5,7,9-11. Here we show that the GRC can also be paternally inherited. Confocal microscopy using GRC-specific FISH probes indicated that a considerable fraction of sperm heads (1-19%) in zebra finch ejaculates still contained the GRC. In line with these cytogenetic data, sequencing of ejaculates revealed that individual males from two families differed strongly and consistently in the number of GRCs in their ejaculates. Examining a captive-bred population of hybrids of the two zebra finch subspecies (T. g. guttata and T. g. castanotis) revealed that the descendants inherited their mitochondria from a castanotis mother but their GRC from a guttata father. Moreover, GRC haplotypes across nine different castanotis matrilines showed at best a weak tendency to be co-inherited with mtDNA haplotypes. Within castanotis, the GRC showed little variability, while the mtDNA of matrilines was highly divergent. This suggests that a single GRC haplotype has recently spread across the entire castanotis population, crossing the matriline boundaries via paternal spillover. Our findings raise the possibility that certain GRC haplotypes could selfishly spread through the population, via additional paternal transmission, thereby outcompeting other GRC haplotypes that were limited to strict maternal inheritance, even if this was partly detrimental to organismal fitness.

genomics↗

bioRxiv2020

A global analysis of song frequency in passerines provides no support for the acoustic adaptation hypothesis but suggests a role for sexual selection

Many animals use acoustic signals for communication, implying that the properties of these signals can be under strong selection. The acoustic adaptation hypothesis predicts that species living in dense habitats emit lower-frequency sounds than those in open areas, because low-frequency sounds generally propagate further in denser vegetation. Signal frequency may also be under sexual selection, because it correlates with body size and lower-frequency sounds are perceived as more intimidating. Here, we evaluate these hypotheses by analysing variation in peak song frequency across 5,085 passerine species (Passeriformes). A phylogenetically-informed analysis revealed that song frequency decreases with increasing body mass and with male-biased sexual size dimorphism. However, we found no support for the predicted relationship between frequency and habitat. Our results suggest that the global variation in passerine song frequency is mostly driven by natural and sexual selection causing evolutionary shifts in body size rather than by habitat-related selection on sound propagation. Statement of authorshipTA and PM conceived and designed the study with input from all authors. TA and BK coordinated the study. PM collected the song data. MV performed the statistical analyses with input from WF. MB made the figures with help from MV and PM. TP and HB provided bioacoustic expertise. PM drafted the first version of the manuscript. TA, BK and PM revised and finalized the manuscript with input from all authors. Data availability statementThe data used in this study were collected from publicly available databases. All data and computer code used to generate the results, as well as supplementary figures and tables will be freely available at https://osf.io/fa9ky/.

evolutionary biology↗

bioRxiv2020

Offspring performance is well buffered against stress experienced by ancestors

Evolution should render individuals resistant to stress and particularly to stress experienced by ancestors. However, many studies report negative effects of stress experienced by one generation on the performance of subsequent generations. To assess the strength of such transgenerational effects we used a strategy aimed at overcoming the problem of type I errors when testing multiple proxies of stress in multiple ancestors against multiple offspring performance traits, and applied it to a large observational data set on captive zebra finches (Taeniopygia guttata). We combined clear one-tailed hypotheses with steps of validation, meta-analytic summary of mean effect sizes, and independent confirmatory testing. With this approach we assess to what extent offspring performance in adulthood depends on (1) direct effects of own experiences during early development, (2) indirect condition-transfer effects of the early environment experienced by the parents and the grandparents, and (3) beneficial effects of a match between the environments experienced by the offspring and by its parents. Our study shows that drastic differences in early growth conditions (nestling body mass 8 days after hatching varied 7-fold between 1.7 and 12.4 gram) had only moderate direct effects on adult morphology (95%CI: r=0.19-0.27) and small direct effects on fitness traits (r=0.02-0.12). In contrast, we found no indirect effects of parental or grandparental condition (r=-0.017-0.002; meta-analytic summary of 138 effect sizes), and mixed evidence for small benefits of matching environments, as the latter was not robust to confirmatory testing in independent data sets. This study shows that evolution has led to a remarkable robustness of zebra finches against undernourishment and that transgenerational effects are absent. Author SummaryHow the early life conditions of your ancestors might influence your own life, an aspect of epigenetic inheritance, has become a popular topic among evolutionary biologists and has sparked much interest by the general public. Many theoretical and empirical studies have addressed this question, leading to theories of adaptive programming and condition transfer and ideas of epigenetic or genetic organization. Despite the popularity of this topic, however, there is a lack of a standard framework to guide empirical studies, which are at risk of over-interpreting the most significant effects that might emerge by chance alone when conducting a large number of tests. In this study, we used long-term observational data on multiple morphological and life-history traits of hundreds of male and female zebra finches with information on the early life conditions of both the focal birds and their parents and grandparents. This allows us to comprehensively quantify the magnitude of direct and transgenerational effects of early developmental conditions. Our study (1) proposes a standardized statistical framework for future investigations, (2) summarizes the average effect size (in zebra finches) and indicates the sample sizes needed to pick up such an effect, and (3) provides a counter statement to a growing faith in the ubiquity of transgenerational effects despite their limited evolutionary or mechanistic plausibility.

evolutionary biology↗

bioRxiv2019

Proximate causes of infertility and embryo mortality in captive zebra finches

AbstractSome species show high rates of reproductive failure, which is puzzling because natural selection works against such failure in every generation. Hatching failure is common in both captive and wild zebra finches (Taeniopygia guttata), yet little is known about its proximate causes. Here we analyze data on reproductive performance (fate of >23,000 eggs) based on up to 14 years of breeding of four captive zebra finch populations. We find that virtually all aspects of reproductive performance are negatively affected by inbreeding (mean r = -0.117), by an early-starting, age-related decline (mean r = -0.132), and by poor early-life nutrition (mean r = - 0.058). However, these effects together explain only about 3% of the variance in infertility, offspring mortality, fecundity and fitness. In contrast, individual repeatability of different fitness components varied between 15% and 50%. As expected, we found relatively low heritability in fitness components (median: 7% of phenotypic, and 29% of individually repeatable variation). Yet, some of the heritable variation in fitness appears to be maintained by antagonistic pleiotropy (negative genetic correlations) between male fitness traits and female and offspring fitness traits. The large amount of unexplained variation suggests a potentially important role of local dominance and epistasis, including the possibility of segregating genetic incompatibilities.

evolutionary biology↗

bioRxiv2019

A sex chromosome inversion is associated with copy number variation of mitochondrial DNA in zebra finch sperm

Propulsion of sperm cells via movement of the flagellum is of vital importance for successful fertilization. Presumably, the energy for this movement comes from the mitochondria in the sperm midpiece. Larger midpieces may contain more mitochondria, which should enhance the energetic capacity and hence promote mobility. Due to an inversion polymorphism on their sex chromosome TguZ, zebra finches (Taeniopygia guttata castanotis) exhibit large within-species variation in sperm midpiece length, and those sperm with the longest midpieces swim the fastest. Here, we test through quantitative real-time PCR in zebra finch ejaculates whether the inversion genotype has an effect on the copy number of mitochondrial DNA. Taking the inversion genotype as a proxy for midpiece length, we find that zebra finches with longer midpieces indeed have more copies of the mitochondrial DNA in their ejaculates than those with shorter midpieces, with potential downstream effects on the rate of ATP production and sperm swimming speed. This study sheds light on the proximate cause of a fitness-relevant genetic polymorphism, suggesting the involvement of central components of gamete energy metabolism.\n\nData availabilitySupplementary data file

evolutionary biology↗

bioRxiv2019

The role of genetic constraints and social environment in explaining female extra-pair mating

Why females of socially monogamous species copulate with males other than their partner has been a long-standing, unresolved puzzle. We previously reported that female promiscuity appears to be a genetic corollary of male promiscuity (intersexual pleiotropy hypothesis). Here we put this earlier finding to a critical test using the same population of zebra finches Taeniopygia guttata. After three generations of artificial selection on male courtship rate, a correlate of extra-pair mating, we assess whether female promiscuity changed by indirect selection and we re-examine the crucial genetic correlations. Our new analyses with substantially increased statistical power clearly reject the hypothesis that male and female promiscuity are genetically homologous traits. Our study highlights that individual females show low repeatability in extra-pair mating behavior across different social environments. This emphasizes the potential importance of pair bond strength and the availability of favored extra-pair males as factors explaining variation in patterns of female promiscuity.

evolutionary biology↗

bioRxiv2018

Violating the normality assumption may be the lesser of two evils

When data are not normally distributed (e.g. skewed, zero-inflated, binomial, or count data) researchers are often uncertain whether it may be legitimate to use tests that assume Gaussian errors (e.g. regression, t-test, ANOVA, Gaussian mixed models), or whether one has to either model a more specific error structure or use randomization techniques.Here we use Monte Carlo simulations to explore the pros and cons of fitting Gaussian models to non-normal data in terms of risk of type I error, power and utility for parameter estimation.We find that Gaussian models are remarkably robust to non-normality over a wide range of conditions, meaning that P-values remain fairly reliable except for data with influential outliers judged at strict alpha levels. Gaussian models also perform well in terms of power and they can be useful for parameter estimation but usually not for extrapolation. Transformation of data before analysis is often advisable and visual inspection for outliers and heteroscedasticity is important for assessment. In strong contrast, some non-Gaussian models and randomization techniques bear a range of risks that are often insufficiently known. High rates of false-positive conclusions can arise for instance when overdispersion in count data is not controlled appropriately or when randomization procedures ignore existing non-independencies in the data.Overall, we argue that violating the normality assumption bears risks that are limited and manageable, while several more sophisticated approaches are relatively error prone and difficult to check during peer review. Hence, as long as scientists and reviewers are not fully aware of the risks, science might benefit from preferentially trusting Gaussian mixed models in which random effects account for non-independencies in the data in a transparent way.Tweetable abstract Gaussian models are remarkably robust to even dramatic violations of the normality assumption.Competing Interest StatementThe authors have declared no competing interest.View Full Text

scientific communication and education↗

bioRxiv2018

Programmed DNA elimination of germline development genes in songbirds

Genomes can vary within individual organisms. Programmed DNA elimination leads to dramatic changes in genome organisation during the germline-soma differentiation of ciliates1, lampreys2, nematodes3,4, and various other eukaryotes5. A particularly remarkable example of tissue-specific genome differentiation is the germline-restricted chromosome (GRC) in the zebra finch which is consistently absent from somatic cells6. Although the zebra finch is an important animal model system7, molecular evidence from its large GRC (>150 megabases) is limited to a short intergenic region8 and a single mRNA9. Here, we combined cytogenetic, genomic, transcriptomic, and proteomic evidence to resolve the evolutionary origin and functional significance of the GRC. First, by generating tissue-specific de-novo linked-read genome assemblies and re-sequencing two additional germline and soma samples, we found that the GRC contains at least 115 genes which are paralogous to single-copy genes on 18 autosomes and the Z chromosome. We detected an amplification of [≥]38 GRC-linked genes into high copy numbers (up to 308 copies) but, surprisingly, no enrichment of transposable elements on the GRC. Second, transcriptome and proteome data provided evidence for functional expression of GRC genes at the RNA and protein levels in testes and ovaries. Interestingly, the GRC is enriched for genes with highly expressed orthologs in chicken gonads and gene ontologies involved in female gonad development. Third, we detected evolutionary strata of GRC-linked genes. Developmental genes such as bicc1 and trim71 have resided on the GRC for tens of millions of years, whereas dozens have become GRC-linked very recently. The GRC is thus likely widespread in songbirds (half of all bird species) and its rapid evolution may have contributed to their diversification. Together, our results demonstrate a highly dynamic evolutionary history of the songbird GRC leading to dramatic germline-soma genome differences as a novel mechanism to minimise genetic conflict between germline and soma.

evolutionary biology↗

bioRxiv2018

Avoiding misinterpretation of regression lines in allometry: is sexual dimorphism in digit ratio spurious?

The statistical analysis of allometry (size-dependence of traits) is fraught with difficulty that is often underestimated. In light of some recent controversies about statistical methods and the resulting biological conclusions, I here discuss the interpretation of regression lines and show how to avoid spurious effects. General linear models based on ordinary least square (OLS) regression are often used to quantify sexual dimorphism in a trait of interest that is modelled as a function of sex while controlling for size as a covariate. However, an analysis of artificially generated data where males and females differ in size only, but are otherwise built according to the same principles, shows that the OLS method induces a spurious dimorphism where there is none. Hence, OLS-based general linear models should not be regarded as a fail-proof tool that automatically provides the correct answer to whatever question one has in mind. Here I show how to avoid misinterpretation and how to best proceed with answering the recent debate about sexual dimorphism in digit ratio, a trait that is thought to reflect sex-hormone levels during development. The limited data, currently available to me, suggests that the widely accepted sexual dimorphism in digit ratio might well be only a by-product of an allometric shift in shape, urgently calling for a re-examination in larger data sets on humans and other vertebrates.

zoology↗