Theory predicts that speciation rates should be accelerated in organisms undergoing sexual selection. In systems involving female choice, sexual selection acts directly on traits that may be important in prezygotic reproductive isolation, potentially fostering rapid divergence of such traits among allopatric populations. Despite the appeal of this concept, it has proven difficult to document. We provide genetic, behavioral, and simulation data illustrating that the striking and possibly recent divergence in traits of male behavior and morphology among populations of the jumping spider Habronattus pugillis can be attributed to sexual selection. We have found evidence for varying degrees of lower female response and offspring viability among some betweenpopulation crosses, consistent with the early stages of speciation. We have developed a gene-tree-based method for comparing phenotypic and genetic data sets to infer selection, and have found robust statistical evidence that directional selection has acted on male traits, by confirming that their rate of fixation exceeds that of neutral mitochondrial genes. Because these traits are apparent targets of female choice, the results indicate that sexual selection is driving divergence of phenotypes potentially crucial to the speciation process.A lthough theory predicts that speciation rates should be accelerated in organisms undergoing sexual selection (1-5), obtaining good empirical evidence has many difficulties (reviewed in ref. 6). Ideally, evidence would show that sexual selection has caused divergence among populations, and that the rate of divergence is greater than expected under allopatric speciation without sexual selection. However, because the process of speciation occurs throughout long periods of time, rarely are we able to document ongoing selection while simultaneously observing clade diversification.Previous studies addressing whether sexual selection has influenced rates of diversification have primarily focused on sister clade comparisons. These studies have shown correlations between species diversity and traits believed to be indicators of sexual selection (e.g., sexual dimorphism) on phylogenetic trees (7-10). This correlative phylogenetic approach possesses the virtue of taxonomic breadth, but typically lacks direct population-level evidence that the traits in question have a selective basis. Additionally, factors other than sexual selection, such as high dispersal ability and large, fragmented geographical ranges, have also been correlated with increased species richness (11).Likewise, numerous studies have demonstrated ongoing sexual selection within populations (e.g., refs. 12-14). However, from such results alone it has been difficult to implicate sexual selection directly in increasing the divergence rate between populations, either because of the low number of populations studied or because of the lack of an historical timeframe.Both the comparative phylogenetic approach and the selection-experiment approach are tremendously valuable, but n...
We sequenced the entire mitochondrial genome of the jumping spider Habronattus oregonensis of the arachnid order Araneae (Arthropoda: Chelicerata). A number of unusual features distinguish this genome from other chelicerate and arthropod mitochondrial genomes. Most of the transfer RNA (tRNA) gene sequences are greatly reduced in size and cannot be folded into typical cloverleaf-shaped secondary structures. At least nine of the tRNA sequences lack the potential to form TPsiC arm stem pairings and instead are inferred to have TV-replacement loops. Furthermore, sequences that could encode the 3' aminoacyl acceptor stems in at least 10 tRNAs appear to be lacking, because fully paired acceptor stems are not possible and because the downstream sequences instead encode adjacent genes. Hence, these appear to be among the smallest known tRNA genes. We postulate that an RNA editing mechanism must exist to restore the 3' aminoacyl acceptor stems to allow the tRNAs to function. At least seven tRNAs are rearranged with respect to the chelicerate Limulus polyphemus, although the arrangement of the protein-coding genes is identical. Most mitochondrial protein-coding genes of H. oregonensis have ATN as initiation codons, as commonly found in arthropod mtDNAs, but cytochrome oxidase subunits 2 and 3 genes apparently use TTG as an initiation codon. Finally, many of the gene sequences overlap one another and are truncated. This 14,381-bp genome, the first mitochondrial genome of a spider yet sequenced, is one of the smallest arthropod mitochondrial genomes known. We suggest that posttranscriptional RNA editing can likely maintain function of the tRNAs, while permitting the accumulation of mutations that would otherwise be deleterious. Such mechanisms may have allowed for the minimization of the spider mitochondrial genome.
In island systems with diverging populations, the history of island formation and genealogical estimates of divergence dates can be mutually informative. In the "sky islands" of southeastern Arizona, climate-induced contraction of woodlands appears to have fragmented populations of woodland-dwelling species onto disjunct mountain ranges. Montane populations of the jumping spider, Habronattus pugillis, display striking amounts of phenotypic divergence among ranges. Paleoclimatic estimates date woodland fragmentation at approximately 10,000 years ago, suggesting that phenotypic divergence has been extraordinarily rapid in these spiders. This phylogeographic study of populations of H. pugillis attempts to clarify the species' history of isolation and divergence and to address the suitability of available paleoclimatic data for dating divergences among populations of the region's woodland-dwelling organisms. Mitochondrial sequence data of spiders from 13 mountain ranges was used to reconstruct genealogical relationships. Gene trees show that small mountain ranges tend to have populations whose sequences form monophyletic groups, whereas larger ranges do not. Paraphyly among genes from larger ranges could result from either recent migration or incomplete lineage sorting. I use phylogenetic and geographic information to test these alternatives, and conclude that incomplete lineage sorting best explains the observed paraphyly. Gene trees are concordant with some of the predictions of vegetation history generated by examination of topography. Dates estimated for divergence of populations vary from 30,000 years to more than 2 million years ago, suggesting multiple vicariance events that are older than would be inferred from paleoclimatic studies. These findings illustrate that use of any single paleontological dataset to calibrate molecular clocks can potentially greatly underestimate actual divergence times.
The cloverleaf secondary structure of transfer RNA (tRNA) is highly conserved across all forms of life. Here, we provide sequence data and inferred secondary structures for all tRNA genes from 8 new arachnid mitochondrial genomes, including representatives from 6 orders. These data show remarkable reductions in tRNA gene sequences, indicating that T-arms are missing from many of the 22 tRNAs in the genomes of 4 out of 7 orders of arachnids. Additionally, all opisthothele spiders possess some tRNA genes that lack sequences that could form well-paired aminoacyl acceptor stems. We trace the evolution of T-arm loss onto phylogenies of arachnids and show that a genome-wide propensity to lose sequences that encode canonical cloverleaf structures likely evolved multiple times within arachnids. Mapping of structural characters also shows that certain tRNA genes appear more evolutionarily prone to lose the sequence coding for the T-arm and that once a T-arm is lost, it is not regained. We use tRNA structural data to construct a phylogeny of arachnids and find high bootstrap support for a clade that is not supported in phylogenies that are based on more traditional morphological characters. Together, our data demonstrate variability in structural evolution among different tRNAs as well as evidence for parallel evolution of the loss of sequence coding for tRNA arms within an ancient and diverse group of animals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.