Abstract
Gondwanan vicariance, long‐distance dispersal (LDD), and boreotropical migration have been proposed as alternative hypotheses explaining the pantropical distribution pattern of organisms. In this study, the historical biogeography of the pond skater genus Limnogonus was reconstructed to evaluate the impact of biogeographical scenarios in shaping their modern transoceanic disjunction. We sampled almost 65% of recognized Limnogonus species. Four DNA fragments including 69 sequences were used to reconstruct a phylogram. Divergence time was estimated using a Bayesian relaxed clock method and three fossil calibrations. Diversification dynamics and ancestral area reconstruction were investigated by using maximum likelihood and Bayesian approaches. Our results showed the crown group of Limnogonus originated and diversified in Africa in the early Eocene (49 Ma, HPD: 38–60 Ma), subsequently expanding into other regions via dispersal. The colonization of the New World originated from the Oriental Region probably via the Bering Land Bridge in the late Eocene. Two split events between the Old World and New World were identified: one between Neotropics and Oriental region around the middle Oligocene (30 Ma, HPD: 22–38 Ma), and the other between Neotropics and Africa during the middle Miocene (14 Ma, HPD: 8–21 Ma). The evolutionary history of Limnogonus involved two biogeographical processes. Gondwanan vicariance was not supported in our analyses. The diversification of Limnogonus among Africa, Oriental, and Neotropical regions corresponded with the age of land bridge connection and dispersed as a member associated with the broad boreotropical belt before local cooling (34 Ma). The current transoceanic disjunctions in Limnogonus could be better explained by the disruption of “mixed‐mesophytic” forest belt; however, the direct transoceanic LDD between the Neotropics and Africa could not be ruled out. In addition, the “LDD” model coupled with island hopping could be a reasonable explanation for the diversification of the Oriental and Australian regions during the Oligocene.
Highlights
It was noteworthy that ancestral area reconstruction indicated that the colonization of the New World directly originated from the Oriental Region rather than from much closer Australian Region (Figure 4), which suggested that the diversification of Limnogonus probably dispersed through the Bering Land Bridge (BLB) and migrated into the Neotropical Region rather than by means of direct transoceanic long-d istance dispersal (LDD)
Based on the good dispersal abilities of these three species, the “LDD” model coupled with island hopping could be a reasonable scenario for the diversification of Limnogonus between the Oriental and Australian regions
The pond skater genus Limnogonus presented a strong case in support of the hypothesis in semi-aquatic organisms
Summary
Our ingroup sampling followed the classification of Andersen (1975, 1995), and the dataset included 18 species/subspecies, which represented 58% of the described subgenus Limnogonus s.str. species (11/19) and 67% of the described subgenus Limnogonoides species (6/9) (Table S1). The dynamic rate variation among tree lineages was evaluated using the following approaches in BAMMtools: (1) The mean phylorate plot indicated distinct speciation rates by mapping colors to rates on all branches, (2) macro-evolutionary cohort analysis displayed the pairwise probability that any two species shared a common macro-evolutionary rate dynamic, and (3) the speciation rate, extinction rate, and net diversification rate of Limnogonus were extracted by rate-through-time analysis. As the widespread species of Limnogonus do not occur in more than two of the four regions that we defined, the maximum number of areas assignable to each node was set to two in all analyses. The crown group of clades I, II, and III diversified in the Oriental and Neotropical Regions with subsequent range expansions into Africa via dispersal (node 6; Figure 3b), followed by splits into the Old and New World lineages in the middle Oligocene and middle Miocene, respectively (nodes 8 and 9; Figure 3b). A minimum of two dispersals from the Oriental to Australian Region occurred during the Eocene–Oligocene boundary (node 7; Figure 3b) and formed the clades V and VI, respectively (nodes 12 and 13; Figure 3b)
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