Spider Tree of Life: Spiders are a prototypical highly diverse arthropod group comprising over 45,000 described species. Diversifying since the Devonian, this ancient group plays a dominant predatory role in almost every terrestrial ecosystem. In addition to their remarkable ecological importance, diversity, and abundance, spiders are known for their extraordinary biomolecules like venoms and silks, and have become models for behavioral and evolutionary studies. Despite considerable effort, progress in spider molecular systematics has lagged behind the advances made in other comparable arthropod groups. Unfortunately, this has hindered family-level resolution, classification, and tests of important macroevolutionary hypotheses (e.g., the origin of sticky silks, various web types and hunting strategies).
Future research in my lab will continue to build upon the enormous phylogenomic datasets (both transcriptome and AHE data) currently being gathered to answer longstanding questions regarding the relationships, diversification, and evolution of spiders. Student projects will further our understanding of the spider Tree of Life (both deep and shallow evolutionary time), placing spider evolution in a more robust and confident context.
The evolution of body size: Body size is one of the most important determinants of an organism’s ecological role (Hanken and Wake 1993). The genus Aphonopelma contains 11 species characterized as miniature (Hamilton et al., 2016). This diversity comprises 40% of the total tarantula diversity that can be found in the United States. Perhaps the most interesting observation about this unique lineage, is that everywhere the miniature species are found, they are sympatric with a large species. They are never sympatric with another small species, but large species can be sympatric with multiple miniature species. Often times miniaturization in invertebrates is associated with reduced and simplified adult morphology, with many miniature taxa bearing strong resemblance to the juvenile form of a sister group. However, these hypothesized paedomorphic traits have not yet been investigated using a rigorous phylogenetic comparative framework.
Future research will explicitly test hypotheses that are fundamental to addressing diversification pattern and process within this lineage of miniature Aphonopelma. Additionally, body size appears to be an important variable in the evolutionary arms-race between bats and mots. My current and future research investigates how body size has evolved across the bombycoid moths and whether this is correlated with other anti-bat traits and differences in diversity patterns.
"Nothing in evolution makes sense except when seen in the light of phylogeny."
- Jay Savage, evolutionary biologist."
Understanding how Earth's diversity has been shaped by evolutionary process is one of the key objectives in biological research. Central to this understanding is our ability to confidently infer relationships among taxa across the Tree of Life, explain distribution patterns across differing landscapes and time, and discover how biotic and abiotic factors influence speciation and extinction. Phylogenetic systematics is a powerful approach that provides us the ability to address key questions in the evolution of diversity. With a phylogeny as a framework, we can begin to answer why and how evolution has produced the many forms we see.
My research employs macro- and microevolutionary approaches to address key questions in the evolution of terrestrial arthropod diversity. Using phylogenomics (i.e., developed an Anchored Hybrid Enrichment (AHE) phylogenomic probe set for use across Araneae, utilizing this same methodology in Lepidoptera, and my collaborative endeavors to use AHE and transcriptomics across arthropods), my research seeks to establish well-supported phylogenetic hypotheses, followed by robust, integrative investigations into how evolutionary forces have shaped diversity and the processes driving patterns of biodiversity. While I have an organismal focus on spiders and moths, my research is driven by questions, such as: 1) What are the relationships within the arthropod Tree of Life?; 2) Why are particular lineages on the Tree of Life more diverse than others?; and 3) What specific characters, traits, or interactions have influenced diversification? Below I outline major ongoing projects and my future research plans.
Phylogenomics – Anchored Hybrid Enrichment: Funding from an NSF DDIG provided the opportunity to collaborate with Alan and Emily Lemmon (Florida State University), where we have developed an Anchored Hybrid Enrichment (AHE) probe kit for resolving the spider Tree of Life at multiple evolutionary depths. This approach builds upon the previous AHE vertebrate work, but makes high-throughput targeted sequencing available to non-model organisms and arthropod groups that lack fully assembled, annotated genomes. Due to the ease with which AHE data can be gathered, and its broad applicability across groups, our aim was to provide a mechanism whereby different researchers can confidently and effectively use the same loci for independent projects, yet allow synthesis of data across independent research groups, thereby accelerating an understanding of the Tree of Life. The development of this approach has produced a number of collaborative endeavors with researchers studying a variety of groups across the spider Tree of Life, as well as other arachnid groups (e.g., Opiliones and scorpions). Additionally, my postdoc advisor (Kawahara) has developed an AHE Lepidoptera kit, which I am utilizing to study moth evolution. Currently, we are redesigning this kit to work more effectively within the moth superfamily Bombycoidea. Future work will continue employing this approach towards answering the many fascinating evolutionary questions across arthropods.
Tarantula systematics: My dissertation research documented the taxonomy, diversity, and distribution of the tarantula genus Aphonopelma Pocock, 1901 within the United States. Aphonopelma is a group wherein traditional morphological characters have been shown to be generally ineffective for evaluating inter- and intraspecific variation and provides one of the greatest known challenges to species delimitation in spiders. The principal goal of this research was to formally resolve the group’s species-level diversity by using an explicit phylogenetic approach that integrates molecular data with morphological, geographic, and behavioral data. Using this integrative approach, I taxonomically revised the United States Aphonopelma. The 55 nominal species were synonymized to 16, while 14 new species were described. The vast majority of this diversity can be found in the miniature Aphonopelma (see below) and from the very unique Sky Islands region of the southwestern United States - an area highly vulnerable to climate change, where a number of mountains appear to have endemics losing their habitat.
Future research will broaden this systematic work throughout the family Theraphosidae (tarantulas), resolving relationships and attempting to explain why this group is one of the most diverse of all spiders. Additionally, I plan to expand my previous work by investigating the diversity of Aphonopelma within Mexico, an incredibly diverse region with a large amount of diversity that has been overlooked, undersampled, and undescribed for far too long.
Bat-Moth evolutionary "arms race": Moths and butterflies (Lepidoptera) are hypothesized to have evolved during the angiosperm radiation of the early Cretaceous (146-100 Mya). With an estimated 140,000 described species, an enormous array of wing shapes and body sizes exist across Lepidoptera. However, few studies have investigated the drivers of this spectacular morphological diversity. One intriguing hypothesis I am testing, is that differences in moth wing shape and body size are associated with clade diversity (in particular, the Bombycoidea) and interactions with their primary nocturnal predators – bats; an idea that challenges the conventional hypothesis that angiosperm evolution directly led to moth diversification. Moths possess many different anti-bat traits, including ears keen to a bat's ultrasonic echolocation, acrobatic evasive flight, specialized wing morphology to aid in defensive flight and escape mechanisms (e.g., hindwing tails and forewing lobes), as well as ultrasound-producing organs that "jam" bat biosonar. Bombycoid moths (a group of ~4700 described species), with their suite of anti-predator strategies, are an ideal system to test evolutionary hypotheses concerning the historical path of anti-bat traits. By using the charismatic bombycoid sister lineages - Sphingidae (hawkmoths), and Saturniidae (wild silkmoths) as a model, my research aims to understand whether certain anti-bat strategies have provided the selective advantages needed to increase moth diversity.
My current research program comprises gathering phylogenomic data across the Bombycoidea to infer evolutionary relationships, as well as quantifying body size and wing shape variation, assessing whether lineages possess anti-bat traits, and testing hypotheses on the interplay between wing shape, body size, and anti-bat traits. Future work will continue gathering genomic and morphological data to test whether there are correlated changes between anti-bat strategies and increasing/decreasing rates of speciation or extinction. Additionally, more behavioral studies will be carried out to quantify the selective advantage of anti-bat traits.