ARPHA Conference Abstracts : Conference Abstract
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Conference Abstract
Evolution in Extremis: The When, How, and Why of Hawaiian Carabid Beetles
expand article info James K. Liebherr
‡ Cornell University, Ithaca, United States of America
Open Access

Abstract

The Hawaiian Archipelago is the most isolated oceanic island system in the World, separated from the nearest source areas by more than 4000 km. Five independent colonization events have resulted in diversification of a native carabid beetle fauna in excess of 400 known species. This diverse assemblage is disharmonic, with the major radiations restricted to the platynine genus Blackburnia Sharp (139 species), the subgenus Nesocidium Sharp of Bembidion Latreille (21 species), and the moriomorphine genus Mecyclothorax Sharp (239 species). Biogeographical, ecological, and evolutionary attributes of these three radiations are compared in order to determine factors crucial to carabid beetle diversification in this most-isolated situation. Biogeographical attributes include the age of origin of the constituent radiation, the island likely colonized by its common ancestor, and the biological characteristics, where known, of the colonizing ancestors for each independent radiation. Ecological attributes include the amount of habitat specialization undergone during each radiation, taking into account the primordial habitat colonized and the subsequent pattern of occupation of different habitat types during diversification. Evolutionary attributes include brachyptery, body-size evolution, sexual selection, and the evolution of specialized body conformations. It is shown that ecological specialization—i.e., occupation of a diverse array of ecological zones and microhabitats—in concert with reduced dispersal ability brought on by evolution of brachyptery are positively associated with enhanced levels of diversification. Comparing sympatric island faunas, it is shown that the latter operates synergistically with body size, as the smaller-bodied Mecyclothorax beetles speciate much more rapidly than the larger-bodied Blackburnia on Maui and Hawai῾i Island. Nonetheless, small body size does not gaurantee high diversity, as Bembidion beetles attain body sizes similar to Mecyclothorax beetles. Age of origin of a radiation is a subsidiary criterion for diversification given that the Mecyclothorax radiation commenced only 1.2 Ma, whereas it is hypothesized that Blackburnia have been resident in the Hawaiian archipelago for upwards of 28 Ma. Thus especially for Blackburnia we are constrained in our ability to know all of the evolutionary products of the radiation due to extinction of presumably all or nearly all species that occupied the now-sunken islands northwest of the oldest high island of Kauai. We are fortunate to know of several extinct Blackburnia species discovered in lowland subfossil deposits in Kauai, and these species provide crucial information now regarding future patterns of extinction. Sexual selection can be demonstrated for the Bembidion subgenus Nesocidium, and is a likely explanation for genitalic evolution over parts of the Mecyclothorax radiation, but it is not a phenomenon pervasively associated with increased levels of speciation.

Keywords

biogeography, body size, cryptic species, dispersal, sexual selection, speciation, vicariance

Presenting author

James K. Liebherr

Presented at

19th ECM oral communication

Acknowledgements

I thank collaborators Dan A. Polhemus, Curtis P. Ewing, Arthur Medeiros, David Kavanaugh, Will Haines, and Paul Krushelnycky for sharing specimens and for their hard work in the field.

Hosting institution

Department of Entomology, Cornell University, Ithaca, NY 14853-2601, U.S.A

Author contributions

The author served as primary investigator and senior author on all aspects of the reported research.

Conflicts of interest

The author reports no conflicts of interest for this research.