My current research interests stem from my desire to understand fundamental aspects of biological diversity. These fundamental aspects include the relationships of organisms and their morphological complexity. I study these aspects using phylogenetic systematics and geometric morphometrics. These tools allow us to understand broader themes such as historical biogeography, molecular evolution, conservation and the evolution of morphological diversity.
Systematics
Part of my current research focus is to resolve some of the difficult phylogenetic problems associated with the Indo-Pacific family Leiognathidae. Ponyfishes (as leiognathids are commonly called) have a unique circumesophageal organ that is used to maintain symbiotic bacteria. The fishes co-opt the light produced by the bacteria and use it for photic communication. Males of many species have translucent areas on their flanks that concentrate light to flash to females. I am studying the role of this light organ system in the evolution of these fish. Ultimately, I will resolve many of the taxonomic problems that plague this group by a revision of the entire family using molecular, morphological and behavioral (flashing) characters. Much of this work is associated with the products of recent field trips to Madagascar, Sri Lanka, Indonesia, the Malay Peninsula and Taiwan. The phylogeny being prepared for this family will be used in a series of publications to revise the taxonomy of the group, identify new species, and test hypotheses about the role of sexual selection on morphological diversity and species richness in the family.
Recent Systematics Publications:
-Sparks, J.S., Chakrabarty, P. (2007) A new species of ponyfish (Teleostei:Leiognathidae: Photoplagios) from the Philippines. Copeia 2007 (3): 622-629.
-Chakrabarty, P., Sparks, J.S. (2008) Diagnoses for Leiognathus Lacepède 1802, Equula Cuvier 1815, Equulites Fowler 1904, Eubleekeria Fowler 1904, and a new ponyfish genus (Teleostei: Leiognathidae). American Museum Novitates 3623, 1-11.
-Smith, W.L., Chakrabarty, P., Sparks, J.S., (2008) Phylogeny, taxonomy and evolution of South American cichlids (Percomorpha: Cichlidae: Cichlinae). Cladistics 24, 1-17.
Biogeography
I am also currently interested in the historical biogeography of Neotropical fishes. I have continued my graduate and post-doctoral research building phylogenetic analyses to better understand the biogeographic relationships of Greater Antillean, Middle and South American cichlids. One of the great unknowns in biogeographic studies is the origin of the fauna of these islands and the four different geological blocks that have united to form Central America and the Yucatan. I found evidence through phylogenetic analysis that the origin of the island cichlids is linked to a vicariance event with mainland Middle America in the Eocene. Vicariance was favored over alternatives because both the pattern of the recovered phylogeny and divergence time estimates from a relaxed clock were congruent with this hypothesis. I continue testing these hypotheses and several large-scale cichlid phylogenies that include a much broader sampling of taxa including fossils. I hope to work with additional groups including the families Lepisostidae (gars), Poeciliidae (guppies; mosquito fish), and Cyprinodontidae (pupfishes; killifishes). I would also like to explore the relationships of near shore marine groups such as the Synbranchidae (swamp-eels) and the Bythitidae (viviparous brotulas). As I develop the phylogenies of these Greater Antillean forms, I will also include many of their continental relatives, and study the related biogeography of those landmasses as well. The relationships of each of these groups are unique but all of them can potentially test biogeographic patterns for the region through phylogenetic analyses.
Recent Biogeography Publications:
-Chakrabarty, P. (2004) Cichlid biogeography: comment and review. Fish and Fisheries 5(2): 97-119.
-Chakrabarty, P. (2006) Systematics and Historical Biogeography of Greater Antillean Cichlidae. Molecular Phylogenetics and Evolution 39, 619-627.
Geometric Morphometrics And Analyses of Disparity
I have done a number of non-thesis projects measuring the relative magnitude of morphological diversity as it is distributed among groups. I used geometric morphometric techniques and analyses of disparity to test hypotheses about cichlid morphological evolution. Hypotheses about the origins of various groups can often be tested by quantifying morphological diversity. I researched how African Rift Lake cichlid groups differ in morphological diversity relative to species richness and ecological diversity. Researchers in the past have tied the rich diversity of these cichlids to different evolutionary hypotheses (e.g., microallopatric speciation, sympatric speciation). Some of these evolutionary hypotheses were based on assumptions made about the morphological diversity of some cichlid clades. I quantified morphological diversity to test these subjective hypotheses about the various processes researchers proposed led to different distributions of morphologies. In several cases the initial assumptions of morphological diversity were incorrect, and so the larger hypotheses about evolution had to be questioned. For example, I found there was not a straightforward relationship between ecological attributes of a clade and its morphological diversity. Therefore, ecology alone cannot be the sole factor leading to the different distributions of morphologies. I am currently researching how this tool can be used to test other hypotheses pertaining to morphological diversity; including the correlation between branch length on a molecular phylogeny and conservative or extreme morphologies.
Recent GM Publications:
-Chakrabarty, P. (2005) Testing conjectures about morphological diversity in cichlids of Lakes Malawi and Tanganyika. Copeia 2005 (2): 259-273.
Morphological Studies
Morphological character analyses are essential in phylogenetics and descriptive work to ensure proper diagnoses, taxonomy and rigorous sampling of all phylogentically informative material. As a collections based scientist I will always continue to have morphological systematics as a major part of my research program. Phylogenies that include morphological characters lead to the discovery of morphological synapomorphies that can be used in descriptive works diagnosing novel taxa or higher groups. In the current systematics age that is dominated by molecular phylogenies the utility of morphological analysis is sometimes questioned. One of many examples of the importance of morphological data in this molecular age is in the verification of calibrations. Calibrations based on fossil taxa are widely used to age different nodes in molecular phylogenies. Unfortunately, these fossils are often incorrectly placed on the molecular phylogeny because of the lack of any morphological data from extant taxa in the character matrix. More rigorous and robust conclusions about phylogenies can only be made with the use of morphological data. In my own work on cichlids I carried out a morphological phylogenetic analysis of Middle American taxa that helped place a fossil from Hispaniola to the Nandopsis clade of Greater Antillean cichlids. I diagnosed this genus based on morphological features and was able to use the fossil (now correctly assigned) as a calibration point. This fossil calibration provided a minimum age for these island cichlids on my molecular biogeographic analysis of Neotropical cichlids.
Recent Morphological Publications:
-Chakrabarty, P. (2006) Taxonomic status of the Hispaniolan Cichlidae. Occasional Papers of the Museum of Zoology, University of Michigan 737: 1 – 16.
-Chakrabarty, P. (2007) A morphological phylogenetic analysis of
Middle American cichlids with special emphasis on the section "Nandopsis"; sensu Regan. Miscellaneous Publications, Museum of Zoology, University of Michigan 198: 1-31.
-Chakrabarty, P., Sparks, J.S. (2007) Phylogeny and taxonomic revision of Nuchequula Whitley 1932 (Teleostei: Leiognathidae), with the description of a new species. American Museum Novitates 3588:1-28.
