Biology subjects

McGuigan, K.

Publications and source records attributed to McGuigan, K..

5 recordsLinked to original sources

bioRxiv2023

Variability of morphology-performance relationships under acute exposure to different temperatures in three strains of zebrafish.

Locomotion is thermally sensitive in ectotherms and therefore it is typically expressed differently among thermally heterogenous environments. Locomotion is a complex function, and while physiological and behavioural traits that influence locomotor performance may respond to thermal variation throughout life, other contributing traits, like body shape, may have more restricted responses. How morphology affects locomotor performance under variable temperature conditions is unknown. Here, we investigated three genetically distinct strains of zebrafish (AB, WIK, and Tu) with a shared multi-generational history at 28{degrees}C. After rearing fish at a constant 28{degrees}C, we measured prolonged swimming speed (Ucrit) at each of six temperatures (between 16{degrees}C and 34{degrees}C). Speed was strongly positively correlated among temperatures, resulting in most among-individual variation being temperature-independent (i.e., fish were relatively fast or slow across all temperatures). However, we also detected significant variation along two axes reflecting temperature-dependent variation, including one reflecting differences among individuals consistent with a hotter-colder tradeoff (i.e., individuals that were relatively fast at cooler temperatures were relatively slow at hotter temperatures and vice versa). Although strains differed in mean swimming performance, within strain (among-individual) patterns of speed variation were markedly consistent. Body shape and size explained significant variation among individuals in both temperature-independent and temperature-dependent axes of swimming speed variation. Notably, morphological traits that were most strongly associated with temperature-independent performance variation (i.e., faster-slower) differed from those associated with temperature-dependent (i.e., hotter-colder) variation. Further, there were significant differences among strains in both the direction and strength of association for specific morphological traits. Our results suggest that thermally heterogenous environments could have complex effects on the evolution of traits that contribute to whole organism performance traits.

zoology↗

bioRxiv2023

Using inbreeding to test the contribution of non-additive genetic effects to additive genetic variance: a case study in Drosophila serrata

Additive genetic variance, VA, is the key parameter for predicting adaptive and neutral phenotypic evolution. Changes in demography (e.g., increased close-relative inbreeding) can alter VA, but how depends on the, typically unknown, gene action and allele frequencies across many loci. For example, VA increases proportionally with the inbreeding coefficient when allelic effects are additive, but larger (or smaller) increases can occur when allele frequencies are unequal at causal loci with dominance effects. Here, we describe an experimental approach to assess the potential for rare, recessive alleles to inflate VA under inbreeding. Applying a powerful paired pedigree design in Drosophila serrata, we measured 11 wing traits on half-sibling families bred via either random or sibling mating, differing only in homozygosity (not allele frequency). Despite close inbreeding and substantial power to detect small VA, we detected no deviation from the expected additive effect of inbreeding on genetic (co)variances. Our results suggest the average dominance coefficient is very small relative to the additive effect, or that allele frequencies are relatively equal at loci affecting wing traits. We outline the further opportunities for this paired pedigree approach to reveal the characteristics of VA, providing insight into historical selection and future evolutionary potential.

evolutionary biology↗

bioRxiv2022

The contribution of mutation to variation in temperature-dependent sprint speed in zebrafish, Danio rerio

The contribution of new mutations to phenotypic variation, and the consequences of this variation for individual fitness, are fundamental concepts for understanding genetic variation and adaptation. Here, we investigated how mutation influenced variation in a complex trait in zebrafish, Danio rerio. Typical of many ecologically relevant traits in ectotherms, swimming speed in fish is temperature-dependent, with evidence of adaptive evolution of thermal performance. We chemically induced novel germline point mutations in males, and measured sprint speed in their sons at six temperatures (between 16{degrees}C and 34{degrees}C). Mutational effects on speed were strongly positively correlated among temperatures, resulting in statistical support for only a single axis of mutational variation, reflecting temperature-independent variation in speed (faster-slower mode). While these results suggest pleiotropic effects on speed across different temperatures, when mutation have consistent directional effects on each trait, spurious correlations arise via linkage, or heterogeneity in mutation number. However, mutation did not change mean speed, indicating no directional bias in mutational effects. The results contribute to emerging evidence that mutations may predominantly have synergistic cross-environment effects, in contrast to conditionally neutral or antagonistic effects which underpin thermal adaptation. However, aspects of experimental design might limit resolution of mutations with non-synergistic effects.

evolutionary biology↗

bioRxiv2022

Maintenance of quantitative genetic variance in complex, multi-trait phenotypes: The contribution of rare, large effect variants in two Drosophila species

The interaction of evolutionary processes to determine quantitative genetic variation has implications for contemporary and future phenotypic evolution, as well as for our ability to detect causal genetic variants. While theoretical studies have provided robust predictions to discriminate among competing models, empirical assessment of these has been limited. In particular, theory highlights the importance of pleiotropy in resolving observations of selection and mutation, but empirical investigations have typically been limited to few traits. Here, we applied high dimensional Bayesian Sparse Factor Genetic modelling to 3,385 gene expression traits from Drosophila melanogaster and from D. serrata to explore how genetic variance is distributed across high-dimensional phenotypic space. Surprisingly, most of the heritable trait covariation was due to few lines (genotypes) with extreme (>3 IQR from the median) values. This observation, in the two independently sampled species, suggests that the House of Cards (HoC) model might apply not only to individual expression traits, but also to emergent co-expression phenotypes. Intriguingly, while genotypes extreme for a multivariate factor also tended to have a higher proportion of individual traits that were extreme, we also observed genotypes that were outliers for multivariate factors but not for any individual traits. We observed other consistent differences between heritable multivariate factors with outlier lines versus those factors that conformed to a Gaussian distribution of genetic effects, including differences in gene functions. We use these observations to identify further data required to advance our understanding of the evolutionary dynamics and nature of standing genetic variation for quantitative traits.

genetics↗

bioRxiv2021

Causes of variability in estimates of mutational variance from mutation accumulation experiments

Characteristics of the new phenotypic variation introduced via mutation have broad implications in evolutionary and medical genetics. Standardised estimates of this mutational variance, VM, span two orders of magnitude, but the causes of this remain poorly resolved. We investigated estimate heterogeneity using two approaches. First, meta-analyses of ~150 estimates from 37 mutation accumulation (MA) studies did not support a difference among taxa (which differ in mutation rate) in standardised VM, but provided equivocal support for standardised VM to vary with trait type (life history versus morphology, predicted to differ in mutation rate). Notably, several experimental factors were confounded with taxon and trait, and further empirical data are required to resolve their influences. Second, we analysed morphological data from an experiment in Drosophila serrata to determine the potential for unintentional heterogeneity among environments in which phenotypes were measured (i.e., among laboratories or time points) or transient segregation of mutations within MA lines to affect standardised VM. Approximating the size of an average MA experiment, variability among repeated estimates of (accumulated) mutational variance was comparable to variation among published estimates of standardised VM for morphological traits. This heterogeneity was (partially) attributable to unintended environmental variation or within line segregation of mutations only for wing size, not wing shape traits. We conclude that sampling error contributed substantial variation within this experiment, and infer that it will also contribute substantially to differences among published estimates. We suggest a logistically permissive approach to improve the precision of estimates, and consequently our understanding of the dynamics of mutational variance of quantitative traits.

genetics↗