Abstract
Abstract:
It is now rare to find a semi-aquatic organism group with which to vigorously test whether their diversification model and distribution pattern are closely related to the Cenozoic temperature variation. This hypothesis is explored for water striders of the genera Aquarius Schellenberg, Gerris Fabricius and Limnoporus Stål, which comprise a monophyletic clade with primarily Holarctic distribution. We sample almost 90% of the currently recognized Aquarius, Gerris and Limnoporus species. Five DNA fragments from 62 species are used to reconstruct a phylogram. Divergence time is estimated using Bayesian relaxed-clock method and three fossil calibrations. We investigate diversification dynamics, biogeography and ancestral state reconstruction by using maximum-likelihood, Bayesian and parsimony approaches. Our results showed that the crown of the three genera originated and underwent an initial diversification in Asia at 72 Ma (HPD: 59-86 Ma) in the Late Cretaceous, subsequently expanding into other regions via dispersal. The Bering Land Bridge was the major migration route between Eurasia and North America but was interrupted before the early Oligocene (34 Ma). Ancestors most likely used lentic habitats, and a minimum of two independent shifts to lotic habitats occurred in the initial diversification. Cenozoic temperature variation regulated the evolutionary history of Holarctic water striders of the genera Aquarius, Gerris and Limnoporus. Temperature warming during Stage I (52-66 Ma) was associated with the disappearance of shallow lentic habitats; this phenomenon forced certain lentic lineages to colonize new lotic habitats and promoted the diversification of lineages. Temperature cooling during Stage II (after 34 Ma) was associated with the fragmentation of water habitats of the 'mixed-mesophytic' belt, resulting in the extinction of historical taxa and influencing close lineages that shaped the present disjunct Eurasian-North American distribution. [ABSTRACT FROM AUTHOR]
