Proceedings. Biological sciences / The Royal Society, Jan 22, 2015
Host shifts and subsequent adaption to novel host plants are important drivers of speciation amon... more Host shifts and subsequent adaption to novel host plants are important drivers of speciation among phytophagous insects. However, there is considerably less evidence for host plant-mediated speciation in the absence of a host shift. Here, we investigated divergence of two sympatric sister elm leaf beetles, Pyrrhalta maculicollis and P. aenescens, which feed on different age classes of the elm Ulmus pumila L. (seedling versus adult trees). Using a field survey coupled with preference and performance trials, we show that these beetle species are highly divergent in both feeding and oviposition preference and specialize on either seedling or adult stages of their host plant. An experiment using artificial leaf discs painted with leaf surface wax extracts showed that host plant chemistry is a critical element that shapes preference. Specialization appears to be driven by adaptive divergence as there was also evidence of divergent selection; beetles had significantly higher survival and ...
Yuccas and their pollinator moths are a textbook example of mutualism, yet we lack sufficiently v... more Yuccas and their pollinator moths are a textbook example of mutualism, yet we lack sufficiently variable markers to properly study the population genetics of the plants. We characterized 13 polymorphic microsatellite loci for Yucca filamentosa by screening primers derived from an expressed sequence tag database. We found four to 13 alleles per locus and the observed heterozygosity ranged from 0.31 to 1. These markers will be useful in future ecological studies of Y. filamentosa.
The interaction between yuccas and yucca moths has been central to understanding the origin and l... more The interaction between yuccas and yucca moths has been central to understanding the origin and loss of obligate mutualism and mutualism reversal. Previous systematic research using mtDNA sequence data and characters associated with genitalic morphology revealed that a widespread pollinator species in the genus Tegeticula was in fact a complex of pollinator species that differed in host use and the placement of eggs into yucca flowers. Within this mutualistic clade two nonpollinating "cheater" species evolved. Cheaters feed on yucca seeds but lack the tentacular mouthparts necessary for yucca pollination. Previous work suggested that the species complex formed via a rapid radiation within the last several million years. In this study, we use an expanded mtDNA sequence data set and AFLP markers to examine the phylogenetic relationships among this rapidly diverging clade of moths and compare these relationships to patterns in genitalic morphology. Topologies obtained from analyses of the mtDNA and AFLP data differed significantly. Both data sets, however, corroborated the hypothesis of a rapid species radiation and suggested that there were likely two independent species radiations. Morphological analyses based on oviposition habit produced species groupings more similar to the AFLP topology than the mtDNA topology and suggested the two radiations coincided with differences in oviposition habit. The evolution of cheating was reaffirmed to have evolved twice and the closest pollinating relative for one cheater species was identified by both mtDNA and AFLP markers. For the other cheater species, however, the closest pollinating relative remains ambiguous, and mtDNA, AFLP, and morphological data suggest this cheater species may be diverged based on host use. Much of the divergence in the species complex can be explained by geographic isolation associated with the evolution of two oviposition habits.
Tegeticula maculata is one of the most ancient and morphologically variable lineages within the y... more Tegeticula maculata is one of the most ancient and morphologically variable lineages within the yucca moths, yet has apparently undergone little diversification in comparison with much younger yucca moth lineages that have rapidly diversified. A phylogeographic approach was used to determine the number of independent lineages within T. maculata and to examine whether these patterns corresponded with morphological differences between its subspecies maculata and extranea. Phylogenetic analysis of mitochondrial DNA sequence variation indicated that the two subspecies are in separate clades, but there was also an equally deep split within subspecies maculata. There was no evidence for gene flow among regions and there was considerable substructure within clades. The phylogeographic structure of moth populations among and within subspecies can be explained in part by historical biogeographic boundaries and increasingly patchy postglacial distribution of the exclusive host plant, Hesperoyucca whipplei. Local specialization and co-adaptation would be possible in the absence of apparent gene flow, yet gross morphological divergence is limited to the very old split between the subspecies. Sorting of ancient mitochondrial lineages followed by local genetic differentiation may explain the pattern of high genetic structure with limited speciation.
... a high level of endemism, especially of plants, and covers areas along the Lake Wales Ridge o... more ... a high level of endemism, especially of plants, and covers areas along the Lake Wales Ridge of central Florida (Estill & Cruzan 2001 ... Finally, we compared parasitoid species diversity between ABS and PL via the Shannon-Wiener index (a joint measure of species richness and ...
Mutualistic interactions can be exploited by cheaters that take the rewards offered by mutualists... more Mutualistic interactions can be exploited by cheaters that take the rewards offered by mutualists without providing services in return. The evolution of cheater species from mutualist ancestors is thought to be possible under particular ecological conditions. Here we provide a test of the first explicit model of the transition from mutualism to antagonism. We used the obligate pollination mutualism between yuccas and yucca moths to examine the origins of a nonpollinating cheater moth, Tegeticula intermedia, and its pollinating sister species, T. cassandra. Based on geographic distribution and ecological factors affecting the pollinators, previous research had indicated that the cheaters evolved in Florida as a result of sympatry of T. cassandra and another pollinator species. We used mitochondrial DNA (mtDNA) sequences and amplified fragment length polymorphism (AFLP) data to investigate the phylogeographic history of the pollinator-cheater sister pair and to test whether the cheaters arose in Florida. Contrary to predictions, phylogenetic and population genetic analyses suggested that the cheaters evolved in the western United States and subsequently spread eastward. Western populations of cheaters had the most ancestral haplotypes and the highest genetic diversity, and there was also significant genetic structure associated with a geographic split between eastern and western populations. In comparison, there was evidence for weak genetic structure between northern and southern pollinator populations, suggesting a long history in Florida. The western origin of the cheaters indicated that the pollinators have more recently become restricted to the southeastern United States. This was supported by AFLP analyses that indicated that the pollinators were more closely related to the western cheaters than they were to geographically proximate cheaters in the east. Shared mtDNA between pollinators and eastern cheaters suggested hybridization, possibly in a secondary contact zone. The results negate the out-of-Florida hypothesis and reveal instead a long, complex, and disparate history for the pollinator-cheater sister pair.
Proceedings. Biological sciences / The Royal Society, Jan 22, 2015
Host shifts and subsequent adaption to novel host plants are important drivers of speciation amon... more Host shifts and subsequent adaption to novel host plants are important drivers of speciation among phytophagous insects. However, there is considerably less evidence for host plant-mediated speciation in the absence of a host shift. Here, we investigated divergence of two sympatric sister elm leaf beetles, Pyrrhalta maculicollis and P. aenescens, which feed on different age classes of the elm Ulmus pumila L. (seedling versus adult trees). Using a field survey coupled with preference and performance trials, we show that these beetle species are highly divergent in both feeding and oviposition preference and specialize on either seedling or adult stages of their host plant. An experiment using artificial leaf discs painted with leaf surface wax extracts showed that host plant chemistry is a critical element that shapes preference. Specialization appears to be driven by adaptive divergence as there was also evidence of divergent selection; beetles had significantly higher survival and ...
Yuccas and their pollinator moths are a textbook example of mutualism, yet we lack sufficiently v... more Yuccas and their pollinator moths are a textbook example of mutualism, yet we lack sufficiently variable markers to properly study the population genetics of the plants. We characterized 13 polymorphic microsatellite loci for Yucca filamentosa by screening primers derived from an expressed sequence tag database. We found four to 13 alleles per locus and the observed heterozygosity ranged from 0.31 to 1. These markers will be useful in future ecological studies of Y. filamentosa.
The interaction between yuccas and yucca moths has been central to understanding the origin and l... more The interaction between yuccas and yucca moths has been central to understanding the origin and loss of obligate mutualism and mutualism reversal. Previous systematic research using mtDNA sequence data and characters associated with genitalic morphology revealed that a widespread pollinator species in the genus Tegeticula was in fact a complex of pollinator species that differed in host use and the placement of eggs into yucca flowers. Within this mutualistic clade two nonpollinating "cheater" species evolved. Cheaters feed on yucca seeds but lack the tentacular mouthparts necessary for yucca pollination. Previous work suggested that the species complex formed via a rapid radiation within the last several million years. In this study, we use an expanded mtDNA sequence data set and AFLP markers to examine the phylogenetic relationships among this rapidly diverging clade of moths and compare these relationships to patterns in genitalic morphology. Topologies obtained from analyses of the mtDNA and AFLP data differed significantly. Both data sets, however, corroborated the hypothesis of a rapid species radiation and suggested that there were likely two independent species radiations. Morphological analyses based on oviposition habit produced species groupings more similar to the AFLP topology than the mtDNA topology and suggested the two radiations coincided with differences in oviposition habit. The evolution of cheating was reaffirmed to have evolved twice and the closest pollinating relative for one cheater species was identified by both mtDNA and AFLP markers. For the other cheater species, however, the closest pollinating relative remains ambiguous, and mtDNA, AFLP, and morphological data suggest this cheater species may be diverged based on host use. Much of the divergence in the species complex can be explained by geographic isolation associated with the evolution of two oviposition habits.
Tegeticula maculata is one of the most ancient and morphologically variable lineages within the y... more Tegeticula maculata is one of the most ancient and morphologically variable lineages within the yucca moths, yet has apparently undergone little diversification in comparison with much younger yucca moth lineages that have rapidly diversified. A phylogeographic approach was used to determine the number of independent lineages within T. maculata and to examine whether these patterns corresponded with morphological differences between its subspecies maculata and extranea. Phylogenetic analysis of mitochondrial DNA sequence variation indicated that the two subspecies are in separate clades, but there was also an equally deep split within subspecies maculata. There was no evidence for gene flow among regions and there was considerable substructure within clades. The phylogeographic structure of moth populations among and within subspecies can be explained in part by historical biogeographic boundaries and increasingly patchy postglacial distribution of the exclusive host plant, Hesperoyucca whipplei. Local specialization and co-adaptation would be possible in the absence of apparent gene flow, yet gross morphological divergence is limited to the very old split between the subspecies. Sorting of ancient mitochondrial lineages followed by local genetic differentiation may explain the pattern of high genetic structure with limited speciation.
... a high level of endemism, especially of plants, and covers areas along the Lake Wales Ridge o... more ... a high level of endemism, especially of plants, and covers areas along the Lake Wales Ridge of central Florida (Estill & Cruzan 2001 ... Finally, we compared parasitoid species diversity between ABS and PL via the Shannon-Wiener index (a joint measure of species richness and ...
Mutualistic interactions can be exploited by cheaters that take the rewards offered by mutualists... more Mutualistic interactions can be exploited by cheaters that take the rewards offered by mutualists without providing services in return. The evolution of cheater species from mutualist ancestors is thought to be possible under particular ecological conditions. Here we provide a test of the first explicit model of the transition from mutualism to antagonism. We used the obligate pollination mutualism between yuccas and yucca moths to examine the origins of a nonpollinating cheater moth, Tegeticula intermedia, and its pollinating sister species, T. cassandra. Based on geographic distribution and ecological factors affecting the pollinators, previous research had indicated that the cheaters evolved in Florida as a result of sympatry of T. cassandra and another pollinator species. We used mitochondrial DNA (mtDNA) sequences and amplified fragment length polymorphism (AFLP) data to investigate the phylogeographic history of the pollinator-cheater sister pair and to test whether the cheaters arose in Florida. Contrary to predictions, phylogenetic and population genetic analyses suggested that the cheaters evolved in the western United States and subsequently spread eastward. Western populations of cheaters had the most ancestral haplotypes and the highest genetic diversity, and there was also significant genetic structure associated with a geographic split between eastern and western populations. In comparison, there was evidence for weak genetic structure between northern and southern pollinator populations, suggesting a long history in Florida. The western origin of the cheaters indicated that the pollinators have more recently become restricted to the southeastern United States. This was supported by AFLP analyses that indicated that the pollinators were more closely related to the western cheaters than they were to geographically proximate cheaters in the east. Shared mtDNA between pollinators and eastern cheaters suggested hybridization, possibly in a secondary contact zone. The results negate the out-of-Florida hypothesis and reveal instead a long, complex, and disparate history for the pollinator-cheater sister pair.
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