Biology subjects

Gibson, M. J. S.

Publications and source records attributed to Gibson, M. J. S..

3 recordsLinked to original sources

bioRxiv2020

Reproductive proteins evolve faster than non-reproductive proteins among Solanum species

Elevated rates of evolution in reproductive proteins are commonly observed in animal species, and are thought to be driven by the action of sexual selection and sexual conflict acting specifically on reproductive traits. Whether similar patterns are broadly observed in other biological groups is equivocal. Here we examine patterns of protein divergence among wild tomato species (Solanum section Lycopersicon), to understand forces shaping the evolution of reproductive genes in this diverse, rapidly evolving plant clade. By comparing rates of molecular evolution among loci expressed in reproductive and non-reproductive tissues, our aims were to test if: a) reproductive-specific loci evolve more rapidly, on average, than non-reproductive loci; male-specific loci evolve at different rates than female-specific loci; c) genes expressed exclusively in gametophytic (haploid) tissue evolve differently from genes expressed in sporophytic (diploid) tissue or in both tissue types; and d) mating system variation (a potential proxy for the expected strength of sexual selection and/or sexual conflict) affects patterns of protein evolution. We observed elevated evolutionary rates in reproductive proteins. However this pattern was most evident for female- rather than male-specific loci, both broadly and for individual loci inferred to be positively selected. These elevated rates might be facilitated by greater tissue-specificity of reproductive proteins, as faster rates were also associated with more narrow expression domains. In contrast we found little evidence that evolutionary rates are consistently different in loci experiencing haploid selection (gametophytic-exclusive loci), or in lineages with quantitatively different mating systems. Overall while reproductive protein evolution is generally elevated in this diverse plant group, some specific patterns of evolution are more complex than those reported in other (largely animal) systems, and include a more prominent role for female-specific loci among adaptively evolving genes.

evolutionary biology↗

bioRxiv2020

Determining the probability of hemiplasy in the presence of incomplete lineage sorting and introgression

AO_SCPLOWBSTRACTC_SCPLOWThe incongruence of character states with phylogenetic relationships is often interpreted as evidence of convergent evolution. However, trait evolution along discordant gene trees can also generate these incongruences - a phenomenon known as hemiplasy. Classic phylogenetic comparative methods do not account for discordance, resulting in incorrect inferences about the number of times a trait has evolved, and therefore about convergence. Biological sources of discordance include incomplete lineage sorting (ILS) and introgression, but only ILS has received theoretical consideration in the context of hemiplasy. Here, we derive expectations for the probabilities of hemiplasy and homoplasy with ILS and introgression acting simultaneously. We find that introgression makes hemiplasy more likely than ILS alone, suggesting that methods that account for discordance only due to ILS will be conservative. We also present a method for making statistical inferences about the relative probabilities of hemiplasy and homoplasy in empirical datasets. Our method is implemented in the software package HeIST (Hemiplasy Inference Simulation Tool), and estimates the most probable number of transitions among character states given a set of relationships with discordance. HeIST can accommodate ILS and introgression simultaneously, and can be applied to phylogenies where the number of taxa makes finding an analytical solution impractical. We apply this tool to two empirical cases of apparent trait convergence in the presence of high levels of discordance, one of which involves introgression between the convergent lineages. In both cases we find that hemiplasy is likely to contribute to the observed trait incongruences.

evolutionary biology↗

bioRxiv2019

A simple genetic architecture and low constraint allows rapid floral evolution in a diverse and recently radiating plant genus

O_LIGenetic correlations among different components of phenotypes, especially resulting from pleiotropy, can constrain (antagonistic) or facilitate (adaptive) trait evolution. These factors could especially influence the evolution of traits that are functionally integrated, such as those comprising the flower. Indeed, pleiotropy is proposed as a main driver of repeated convergent trait transitions, including the evolution of phenotypically-similar pollinator syndromes.\nC_LIO_LIWe assessed the role of pleiotropy in the differentiation of floral and other reproductive traits between two species--Jaltomata sinuosa and J. umbellata (Solanaceae)--that have divergent suites of floral traits consistent with bee- and hummingbird-pollination, respectively. To do so, we generated a hybrid population and examined the genetic architecture (trait segregation and QTL distribution) underlying 25 floral and fertility traits.\nC_LIO_LIWe found that most traits had a relatively simple genetic basis (few, predominantly additive, QTL of moderate to large effect), as well as little evidence of antagonistic pleiotropy (few trait correlations and QTL co-localization, particularly between traits of different classes). However, we did detect a potential case of adaptive pleiotropy among floral size and nectar traits.\nC_LIO_LIThese mechanisms may have facilitated the rapid floral trait evolution observed within Jaltomata, and may be a common component of rapid phenotypic change more broadly.\nC_LI

evolutionary biology↗