Wayne Maddison


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Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Nov 2019)
Mating trait divergence in Habronattus americanus jumping spiders and sex ratio evolution under sexual conflict (2013)

I investigated two topics in evolution. The first concerns the potential role of sexual selection in population divergence of H. americanus jumping spiders. Field observations suggest males seldom feed yet travel widely, apparently seeking mates. Males displayed vigorously to females, whereas females appeared highly choosy. The apparent absence of antagonistic ehavior during male-male interactions suggests mate competition in this species is mediated by female choice. I assessed if female preferences for local males promote reproductive isolation among three H. americanus populations that are each monomorphic for a different male sexual display morph. Supporting this idea, virgin females copulated more often with local compared to foreign males during mate trials. However, the effect of other mating interaction components on mating success remains to be resolved. All crosses produced offspring, ruling out strong intrinsic reproductive barriers among morphs and suggesting divergent female mate preferences may constitute an early source of reproductive isolation. I documented low genetic divergence among several populations, further indicating selection underlies the stark display differences between them. Further, this force appears to counteract gene flow: among-morph population comparisons show “isolation by distance”, despite the fact that phenotypically similar populations, which are scattered widely across the study area, are relatively closely related. This implies a greater exchange of genes between phenotypically similar populations. Collectively, these results implicate divergent selection on, or correlated with, male sexual displays at an early stage of differentiation in this species.In a separate study, two colleagues and I use genetic models to demonstrate that sex ratio adjustment (SRA) by parents can reduce intralocus sexual conflict (IASC) by directing alleles of a sexually antagonistic trait to the sex of offspring they benefit. If the trait is autosomally inherited, this strategy evolves irrespective of which parent’s genotype SRA is based on. It can also evolve when the trait is sex-linked, provided decisions are based on the genotype of the homogametic sex—SRA based on the heterogametic sex instead promotes fixation of the allele that is detrimental to that sex. These results suggest sexual conflict might account for previously unexplained variation in the occurrence of SRA in nature.

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Phylogeny and Systematics of the Jumping Spider Subfamily Euophryinae (Araneae: Salticidae), with Consideration of the Biogeography and Genitalic Evolution (2012)

The Euophryinae is one of the largest subfamilies of jumping spiders (Salticidae) with worldwide distribution. As the only currently recognized salticid subfamily that has diversified almost evenly in both the Old and New World, its historical biogeography is particularly interesting. To clarify the phylogeny of Euophryinae, I amplified and sequenced four genes (nuclear: 28S rDNA, Actin 5C; mitochondrial: 16S-ND1, COI) from 261 jumping spider species, most euophryines, covering all major distribution areas of this subfamily. The molecular phylogeny strongly supports the monophyly of euophryines. Diolenius and its relatives are shown to be euophryines. The phylogeny also indicates euophryines from different continents tend to form their own clades with few cases of mixture. Temporal divergence of Euophryinae was investigated to understand its historical biogeography. The results suggest rapid radiations early during their evolutionary history, with most divergences after the Eocene. Given the age, several intercontinental dispersal events are required to explain the distribution of euophryines. The suggested tolerance to cold may have facilitated early dispersals between the Old and New World through the Antarctic land bridge. I also extensively studied morphological characteristics of a broad range of euophryine genera and species in order to extend our phylogenetic understanding beyond those taxa sampled for molecular data. Systematics of Euophryinae is discussed and a full list of euophryine genera is provided with 122 genera included (34 genera before this study). Euophryine generic groups and redefined delimitations for some genera are reviewed in detail, with 22 new synonyms of genera and 191 new combinations of species proposed. Photographs and illustrations of 173 euophryine species are provided. In addition, 14 new genera and 96 new species of euophryines are described. Correlated evolution between female copulatory duct and male embolus of euophryines was studied in a phylogenetic context. Intra-specific variation of these traits was also examined. The study reveals a positive correlation between the lengths of female copulatory duct and male embolus among euophryine species. However, the inter- and intra-specific variation patterns are not sufficient to tell whether this correlation results from sexual selection or species recognition mechanisms.

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Master's Student Supervision (2010 - 2018)
Phylogenetics and introgression of Habronattus jumping spiders using transcriptomes (Araneae: Salticidae) (2016)

Habronattus is a diverse genus of jumping spiders with complex courtship displays and colourful ornaments in males. A well-resolved species phylogeny would provide an important framework to study these traits, but has not yet been achieved because of conflicting signals from the few genes available. While such discordant gene trees could be the result of deep coalescence in the recently diverged group, there are many indications that hybridization may have occurred and could be the source of conflict. To infer Habronattus phylogenetic relationships and to investigate the cause of gene tree discordance, we assembled transcriptomes for 34 Habronattus species and 2 outgroups. We conducted a concatenated phylogenetic analysis using Maximum Likelihood for 2.41 Mb of nuclear data and for 12.33 kb of mitochondrial data. The concatenated nuclear phylogeny was resolved with high bootstrap support (95-100%) at most nodes with some uncertainty surrounding the relationships of H. icenoglei, H. cambridgei, and H. oregonensis, and Pellenes cf. levii. There are several nodes of the mitochondrial phylogeny that are incongruent to the nuclear phylogeny and indicate possible mitochondrial introgression: the internal relationships of the americanus and the coecatus group, the relationship between the altanus, decorus, banksi, and americanus group, and between H. clypeatus and the coecatus group. To determine the extent of incomplete lineage sorting (ILS) and introgression, we analyzed gene tree discordance for loci longer than 1 kb using Bayesian Concordance Analysis (BCA) for the americanus group (679 loci) and the viridipes/clypeatus/coecatus (VCC) group (517 loci) and found high levels of genetic discordance, especially in VCC group. Finally, we tested specifically for nuclear introgression in the concatenated nuclear matrix with Patterson’s D statistics and DFOIL. We found nuclear introgression resulting in substantial admixture between americanus group species, and between H. sp. (ROBRT) and the clypeatus group, and more minimal nuclear introgression between the clypeatus group and the coecatus group, and between the americanus group and several distant species. Our results indicate that hybridization may have been historically common between phylogenetically distant species of Habronattus, and that reproductive isolation is yet to be complete across the Habronattus phylogeny.

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Intercontinental Ecomorph Convergence in Jumping Spiders (Araneae: Salticidae) (2014)

The ecomorph convergence hypothesis states that the relationship between morphology and ecology will be similar in independently evolved communities. Molecular phylogenetic studies show that most major groups of jumping spiders (Salticidae) are primarily restricted to one continental region, indicating independent replicate radiations. This study asks whether phylogenetically independent communities of salticids predictably converge in morphospace and how likely are they to be influenced by historical contingencies. To test the ecomorph convergence hypothesis, 281 salticid species were collected in two comparable tropical rainforests in Ecuador and Borneo while recording habitat data. Parsimony methods indicate that there are a minimum of 17 evolutionary transitions that have occurred between foliage, ground, and trunk microhabitats. The transitions among all three microhabitats have occurred independently in a major clade of Euophryines, within the Freyines, within the Marpissoids, and within the Amycines. Most of the diversification occurred within continents as the major clades are largely restricted to continental regions. Strict criteria ensuring sufficient sample size, habitat data, and phylogenetic independence in species comparisons resulted in 36 species for all morphometric analyses. Ecomorphs show signs of clustering in multivariate morphological space and there are significant differences in morphology between microhabitats. Trunk salticids have flatter carapaces with shorter legs than ground salticids while foliage salticids have raised carapaces and longer legs when compared to trunk salticids. The relationship between foliage and ground salticids is not as clear. Foliage salticids exhibit the widest range of body forms when compared to the other two ecomorphs. By combining morphometric measurements with molecular phylogenetic data, I show that independent origins of microhabitat use lead to similar body forms providing evidence for the ecomorph convergence hypothesis. However, I also find differences in convergence patterns between continents in terms of the number of shifts between ecomorph origins and species composition between the three microhabitats. These results provide a rare example of a large scale study of intercontinental community-wide patterns that show a mix between convergence and contingency using a comparative phylogenetic framework while demonstrating quantitatively that large scale continental diversifications can behave as predictably as smaller diversifications.

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