DOI: 10.5061/dryad.1vhhmgqs4
title: Regional climates shape the biogeographic history of a broadly distributed freshwater crab species complex

description: Aim: The evolutionary importance of paleoclimate regimes has been noted in
 biogeographic studies. However, little is known about how paleoclimate
 differences shaped the biogeographic pattern and diversification history
 of the freshwater fauna in important zoogeographical boundary regions.
 Here, we aim to investigate how past regional climatic differences have
 shaped the biogeographic history of the inland aquatic fauna in China
 using an endemic freshwater crab species complex found on both sides of
 the Qinling Mountains–Huaihe River Line (QHL), a critical ecological
 boundary in eastern China, as a model system. Location: Eastern China, the
 Qinling Mountains–Huaihe River Line. Taxon: The Sinopotamon yangtsekiense
 species complex. Methods: A total of 482 individuals of Sinopotamon
 yangtsekiense sensu lato were collected from 34 localities throughout its
 entire distributional range. The phylogeographic analyses of population
 structure, morphological and genetic variations, and demographic dynamics
 were made based on multiple mtDNA and nuDNA loci and on morphological
 traits. Fine-tuned ecological niche modeling was used to reconstruct the
 location of climatically suitable areas that existed during the Last
 Glacial Maximum. Results: The divergence of two freshwater crab lineages
 across the QHL correlated with significant past variations in monsoon
 intensity and with the location of multiple refuges. The divergence time
 was broadly consistent with the timing of the critical paleoclimate
 transition event in the mid-Pleistocene (95% HPD, 0.48–1.06 Ma). Each
 freshwater crab lineage has evolved distinct male genital traits
 associated with their isolation in areas with different precipitation
 rates and temperatures in the past. The patterns of crab distribution
 observed today reflect past contractions of the two lineages in response
 to glacial and interglacial cycles during the Pleistocene, followed by
 their subsequent rapid expansion after the Last Glacial Maximum (~15 kya).
 Main conclusions: Populations of the widespread species Sinopotamon
 yangtsekiense s.l. experienced a deep division in the past that led to the
 phylogeographical isolation observed today. The two main drivers of
 genetic isolation in this taxon were (a) differences in the intensity of
 the monsoons on each side of the QHL boundary during
 the mid-Pleistocene, and (b) isolation of different populations
 of S. yangtsekiense s.l. in a number of separate refuges during the LGM.
description: Eight microsatellite loci primers developed by Sun et al. (2009)
 were used for PCR amplification: hxx3, hxx6, hxx7, hxx9, Ga2, Gaca12,
 Gagt21, and Gagt12 (see Table S2 in Supporting Information). Amplification
 conditions are described in Sun et al. (2009). PCR products were separated
 on 6.5% polyacrylamide gels using a LI-COR 4300 automated DNA sequencer
 and analyzed using LI-COR SAGAGT software. The first
 (G1) and second (G2) gonopods of male brachyurans are typically complex
 and exhibit considerable morphological variation among taxa. This is
 especially true in freshwater crabs where the unique shape of the G1 is
 used as a high-weight species-level character in taxonomic identification,
 along with characters of the G2, and the sixth pleonal segment (A6). We
 focused on the morphology of the G1, G2, and A6 of males because of
 difficulties quantifying the characters of the female
 genitalia. Measurements of the subterminal segments (SS) of the G1 and G2
 were made along a straight line beginning at the midpoint of the basal
 margin and ending at the midpoint of the distal margin (at the junction
 between the two parts). Measurements of the terminal articles (TAs) of the
 G1 were made on the ventral side along the midline beginning at the
 midpoint of the junction between the TA basal margin and the distal SS,
 and ending at the TA tip. We measured five morphological traits from 147
 adult male specimens belonging to 27 populations as follows: (a) the G1 SS
 and G1 TA; (b) the G2 SS and G2 TA; (c) the height of the G1TA ventral (V)
 and dorsal (D) lobes; (d) the width (W) and length (L) of the sixth
 pleonal segment (A6); (e) and the angle of the G1TA with respect to the
 longitudinal axis of the G1 and SS (G1 TA angle). G1 TA used the average
 of the V and D. These values were converted into ratios (except the G1 TA
 angle) to exclude errors due to age and size as follows: G1 TA/SS, G2
 TA/SS, G1 TAV/D, and A6 W/L. Coefficients of variation (CV%) were
 determined to indicate morphological variability.