Morphological Evolution

Body Form Evolution

The transition from quadrapedal to limbless body plans has occurred repeatedly in numerous independent lineages of squamates.  However, few genera of lizards possess both fully limbed and limbless species.  The known species-level diversity of skinks of the genus Brachymeles is concentrated in the Philippines, with species exhibiting a full range of limb development, including fully-limbed, intermediate, and limbless forms. The focus of my dissertation study was to investigate the process of limb reduction and loss of Brachymeles using a multi-locus dataset and particularly dense geographic sampling. I was interested in exploring species-level diversity within the group, as well as conducting comprehensive phylogeographic analyses of the group. Given an historical phylogenetic framework, I tested the polarity of evolutionary change in body form, estimated the number of times limbs have been lost in Brachymeles, and surveyed morphological changes associated with limb reduction. The genus Brachymeles has quickly become an excellent model system to address a variety of hypotheses related to body form evolution, miniaturization, limb reduction and loss, and correlated character evolution. Exploring patterns of diversification and body form change within this amazing radiation of lizards resulted in the discovery of many interesting patterns which are summarized in the following two studies:

Siler, C. D. and R. M. Brown.  2011.  Evidence for repeated acquisition and loss of complex body form characters in an insular clade of southeast Asian semi-fossorial skinks.  Evolution 65:2641-2663. PDF

Siler, C. D., A. C. Diesmos, A. C. Alcala, and R. M. Brown.  2011.  Phylogeny of Philippine slender skinks (Scincidae: Brachymeles) reveals underestimated species diversity, complex biogeographical relationships, and cryptic patterns of lineage diversication. Molecular Phylogenetics and Evolution 59:53-65. PDF

Functional Morphology and Evolutionary Genomics

In addition to the studies on the polarity of character change, evolutionary patterns of limb-reduction and loss have provided biologists with a rich suite of hypotheses for tests in a phylogenetic framework. Recent phylogenetic studies have taken comprehensive approaches to understanding the correlated patterns of morphological change, the number of times these changes have taken place, and the directionality of these transitions. For exemplar taxa, a few studies have examined this process from a developmental or functional framework; however, no approaches have been able to take an integrative, multi-taxon approach to studying the process. Recently, I developed a collaborative research proposal that is currently under review at the National Science Foundation. The project will address questions concerning the irreversibility of complex characters via an integrative approach combining the fields of functional morphology and developmental genomics. This project is a collaborative undertaking, involving researchers at Clark University, the University of Massechusetts - Amherst, and Yale University.

Morphological Disparity and Species-level Diversification

I am interested in examining morphological disparity through time and exploring specific components of morphology that have contributed to species-level diversification. Several groups of Philippine vertebrates represent ideal systems for studying these patterns.

The genus Kaloula consists of species of frogs that are commonly referred to as Narrow-Mouth Frogs because of their small, pointed mouths. The diversity of Philippine species is often divided up into three distinct ecomorph groups.  The first being the shrub frogs with species posessing expanded toe disks used for an arboreal lifestyle. The second group consists of burrowing frogs with narrow toe disks who burrow during the year except for the rainy season. Finally, the third group has have evolved a completely arboreal lifestyle.  These species spend their lives within tree-holes and have wide toe disks. I am collaborating on a project investigating the evolution of ecomorph classes among Philippine Kaloula frogs using a phylogenetic framework and dense geographic sampling. We are interested in the amount of morphological change through time and the number of times each ecomorph class evolved.

Agamid lizards in the Philippines represent another system I am currently exploring as part of my research program. Three species are recognized to occur in the Philippines, all with little information available on precise type localities. Variation in crest morphology exists across the Philippines, and I am interested in exploring disparity in crest morphology as it relates to diversification patterns observed across the archipelago.

Phylogenetics and Patterns of Diversification

Over the last few years I have explored the patterns and processes of morphological character evolution and species-level diversification, focusing on understanding the biogeographic and evolutionary histories of Southeast Asian amphibians and reptiles.  Biodiversity in many complex landscapes is likely affected by similar geologic events and climatic changes. I am now pursuing several broader, more comparative approaches to understanding mechanisms driving diversification. I am interested in examining whether numerous lineages are affected similarly in biodiverse areas.  The complex terrain in Southeast Asia represents a perfect model system for investigations of diversification patterns.  The region’s herpetofaunal diversity is highly diverse and endemic; however, few studies to date have taken a comprehensive approach to examining the mechanisms driving species’ diversification.  Projects currently underway combine comparative phylogenetic, ecological modeling, and bioinformatic perspectives in studying the role that geographic and ecological forces play in driving diversification processes.

Phylogeography

Southeast Asia’s complex geological history and highly variable geography and ecology provide an ideal template for testing the effects of geographic change on phylogenetic processes. Within this fascinating region lies the Philippines, an archipelago straddled by the Sundaland-Eurasian and Philippines sea plates, which has been subjected to numerous geological pressures since the beginning of the Mesozoic. Species assemblages in the region have been further shaped by repeated climatological oscillations, primarily since the Pleistocene, wherein fluctuations in sea level caused dramatic changes in the size, connectivity, and presumably the ecological framework of islands.

A component of my research program is interested in employing statistical tests of phylogenetic topology and population genetic analyses of widespread species to explore whether patterns of diversity can be explained by the geologic history of the region or historically accepted models of diversification. This effort has resulted in the observation of numerous fascinating patterns, all of which indicate that the mechanisms driving diversification in the Philippines are far more complex than previously recognized. Some of these patterns are summarized in several of our recent studies:

Conservation Genetics

As part of an international, collaborative effort to develop new conservation methods for the Philippine government, I am working to develop baseline phylogenetic databases for many of the threatened (and heavily traded) reptiles in the Philippines. The PhyloForensic system will provide a means for students, researchers, and government and conservation agencies to better monitor the trade of the country's endemic, flagship species. In addition to providing a new tool for conservation efforts, the datasets will be used to explore and study the distribution of genetic diversity across the landscape, as well as direct conservation priority setting for the protection of genetically unique populations.

Species Delimitation

With the incorporation of molecular data into studies investigating widespread species in Southeast Asia, it has become apparent that we are greatly underestimating species diversity. The repeated observation of deeply divergent and well-supported clades within widespread species of amphibians and reptiles (particularly in the Philippines) has led to a renewed effort in trying to estimate and describe species boundaries. Several projects I am actively working on explore methods for species delimitation using both molecular and morphological data, in an attempt to arrive at well-supported estimates of species diversity.

Biodiversity & Systematics

The regionalized biodiversity across the Philippines is unique.  Levels of endemism among known groups of vertebrates is astonishingly high, with amphibians and reptiles making up the second most diverse vertebrate group in the Philippines. Conservation International classifies the Philippines as both a “Megadiverse” nation and an ecological “Hotspot.” Unfortunately, over the last 75 years, the country has experienced a loss of nearly 90% of its primary rain forest. A component of my research is involved in a massive effort to survey the diversity of amphibians and reptiles across the Philippines. Data resulting from these surveys is being used to direct conservation efforts and identify threatened species. In addition, many of our surveys have resulted in the discovery of new species. Check out a few of our most recent publications here:

Biodiversity Education

Biodiversity Research and Education Outreach - Philippines (PhilBREO) is an international education outreach program I am developing to bring biodiversity information and educational tools to the public using a multi-language and multi-disciplinary approach. This project will develop and implement the PhilBREO website to integrate studies of biodiversity, biogeography, education, and conservation. In addition to biodiversity information focused on species of amphibians and reptiles, the site will provide conservation-based education outreach tools. These tools will range from color photographs taken during biodiversity assessments, simple guides to the amphibian species of each forest site, keys for the identification of each species in the wild, and faunal inventories. These lists will allow for a better public understanding of the distribution of vertebrate diversity in the Philippines.  In addition to English, all printed information in the guides will be translated into Tagalog, the national language of the Philippines, in an effort to engage a greater percentage of communities and organizations in the Philippines.

This effort was recently supported by an Encyclopedia of Life Rubenstein Fellowship aimed at developing species accounts for all amphibians and reptiles in the Philippines. The project has a number of international collaborators, and we welcome anyone interested in getting involved in the effort. The results of this project will be implemented into the PhilBREO website and LifeDesk platform, as well as the databases of our collaborating organizations: Encyclopedia of Life, AmphibiaWeb, The Reptile Database. We encourage you to follow our progress on EOL, the PhilBREO LifeDesk, or our PhilBREO website:

Encyclopedia of Life

PhilBREO LifeDesk

PhilBREO Website (Still under development)

Encyclopedia of Life Rubenstein Fellows Program