Biology subjects

Schwander, T.

Publications and source records attributed to Schwander, T..

5 recordsLinked to original sources

bioRxiv2018

Fundamental and realized feeding niche breadths of sexual and asexual stick-insects

The factors contributing to the maintenance of sex over asexuality in natural populations remain largely unknown. Ecological divergences between lineages with different reproductive modes could help to maintain reproductive polymorphisms, at least transiently, but there is little empirical information on the consequences of asexuality for the evolution of ecological niches. Here, we investigated how niche breadths evolve following transitions from sexual reproduction to asexuality. We estimated and compared the realized feeding niche breadths of five independently derived asexual Timema stick insect species and their sexual relatives. We found that asexual species had a systematically narrower realized niche than sexual species. To investigate how the narrower realized niches of asexual versus sexual species come about, we quantified the breadth of their fundamental niches but found no systematic differences between reproductive modes. The narrow realized niches found in asexuals are therefore likely a consequence of biotic interactions that constrain realized niche size in asexuals more strongly than in sexuals. Interestingly, the fundamental niche was broader in the oldest asexual species compared to its sexual relative. This broad ecological tolerance may help explain how this species has persisted over more than a million years in absence of sex.

ecology↗

bioRxiv2018

Evolutionary dynamics of specialization in herbivorous stick insects

Understanding the evolutionary dynamics underlying herbivorous insect mega-diversity requires investigating the ability of insects to shift and adapt to different host plants. Feeding experiments with nine related stick insect species revealed that insects retain the ability to use ancestral host plants after shifting to novel hosts, with host plant shifts generating fundamental feeding niche expansions. These expansions were not accompanied by expansions of the realized feeding niches however, as species on novel hosts are generally ecologically specialized. For shifts from angiosperm to chemically challenging conifer hosts, generalist fundamental feeding niches even evolved jointly with strong host plant specialization, indicating that host plant specialization is more likely driven by species interactions than by constraints imposed by plant chemistry. By coupling analyses of plant chemical compounds, fundamental and ecological feeding niches in multiple insect species, we provide novel insights into the evolutionary dynamics of host range expansion and contraction in herbivorous insects.

evolutionary biology↗

bioRxiv2018

Genes involved in the convergent evolution of asexuality in stick insects

Asexual reproduction has evolved repeatedly from sexual ancestors across a wide range of taxa. While the costs and benefits associated with asexuality have received considerable attention, the molecular changes underpinning the evolution of asexual reproduction remain relatively unexplored. In particular, it is completely unknown whether the repeated evolution of asexual phenotypes involves similar molecular changes, as previous studies have focused on changes occurring in single lineages. Here we investigate the extent of convergent gene expression changes across five independent transitions to asexuality in stick insects. We compared gene expression of asexual females to females of close sexual relatives in whole-bodies, reproductive tracts, and legs. We identified a striking amount of convergent gene expression change (up to 8% of genes), greatly exceeding that expected by chance. Convergent changes were also tissue-specific, and most likely driven by selection for functional changes. Genes showing convergent changes in the reproductive tract were associated with meiotic spindle formation and centrosome organization. These genes are particularly interesting as they can influence the production of unreduced eggs, a key barrier to asexual reproduction. Changes in legs and whole-bodies were likely involved in female sexual trait decay, with enrichment in terms such as sperm-storage and pigmentation. By identifying changes occurring across multiple independent transitions to asexuality, our results provide a rare insight into the molecular basis of asexual phenotypes and suggest that the evolutionary path to asexuality is highly constrained, requiring repeated changes to the same key genes.

evolutionary biology↗

bioRxiv2017

Sex in the wild: why field-based studies play a critical role in resolving the problem of sex

Why and how sexual reproduction is maintained in natural populations, the so-called \"queen of problems\", is a key unanswered question in evolutionary biology. Recent efforts to solve the problem of sex have often emphasized results generated from laboratory settings. Here, we use a survey of representative \"sex in the wild\" literature to review and synthesize the outcomes of empirical studies focused on natural populations. Especially notable results included relatively strong support for mechanisms involving niche differentiation and a near absence of attention to adaptive evolution. Support for a major role of parasites is largely confined to a single study system, and only three systems contribute most of the support for mutation accumulation hypotheses. This evidence for taxon specificity suggests that outcomes of particular studies should not be more broadly extrapolated without extreme caution. We conclude by suggesting steps forward, highlighting tests of niche differentiation mechanisms in both lab and nature and empirical evaluation of adaptive evolution-focused hypotheses in the wild. We also emphasize the value of leveraging the growing body of genomic resources for non-model taxa to address whether the clearance of harmful mutations and spread of beneficial variants in natural populations proceeds as expected under various hypotheses for sex.\n\nAuthor contributionsSM and MN conceived the paper idea, SM, PM, MN, and TS designed the review strategy, reviewed and analysed the literature, and wrote the manuscript. All authors gave final approval for publication.\n\nData archival locationThe results of our literature survey are provided as electronic supplementary material.

evolutionary biology↗

bioRxiv2017

Effective purifying selection in ancient asexual oribatid mites

Sex is beneficial in the long-term, because it can prevent mutational meltdown through increased effectiveness of selection. This idea is supported by empirical evidence of deleterious mutation accumulation in species with a recent transition to asexuality. Here, we studied the effectiveness of purifying selection in oribatid mites, which have lost sex millions of years ago and diversified into different families and species while reproducing asexually. We compared the accumulation of deleterious coding and non-coding mutations between three asexual and three sexual lineages using transcriptome data. Contrasting studies of young asexual lineages, we find evidence for strong purifying selection that is more effective in asexual compared to sexual oribatid mite lineages. Our results suggest that large populations likely sustain effective purifying selection and facilitate the escape of mutational meltdown in the absence of sex. Thus, sex per se is not a prerequisite for the long-term persistence of animal lineages.

evolutionary biology↗