Marine dispersal and barriers drive Atlantic seahorse diversification

Abstract

Aim To investigate how marine barriers shaped the demographic history of Atlantic seahorses (Syngnathidae: Hippocampus). Location Atlantic Ocean. Methods Range‐wide sampling (n = 390) at mitochondrial and up to five nuclear DNA loci was carried out across the Hippocampus erectus species complex (H. erectus from the Caribbean/North America, H. patagonicus from South America and H. hippocampus from Europe and West Africa). Multi‐species coalescent and approximate Bayesian computation (ABC) frameworks were used to estimate support of competing biogeographical hypotheses and demographic parameters, including lineage divergence times, effective population sizes and magnitudes of population size change. Results We identified four distinct lineages within the H. erectus complex. A posterior probability of 0.626 and corresponding Bayes factors ranging from 3.68 to 11.38 gave moderate to strong support for a basal divergence between South American populations of H. patagonicus and Caribbean/North American populations of H. erectus coincident with the inter‐regional freshwater outflow of the Amazon River Barrier (ARB). Estimates of historical effective population sizes and divergence times indicate that European and West African populations of H. hippocampus expanded after colonization from a more demographically stable Caribbean/North American H. erectus. Main conclusions Our findings of trans‐Atlantic colonization followed by isolation across a deep oceanic divide, and isolation across a freshwater barrier, may demonstrate a contrast in marine divide permeability for this group of rafters. Demographic inference supports the establishment of an ancestral population of the H. erectus complex in the Americas, followed by the ARB splitting it into Caribbean/North and South American lineages at a time of increased sedimentation and outflow. Our estimates suggest that following this split, colonization occurred across the Atlantic via the Gulf Stream currents with subsequent trans‐Atlantic isolation. These results illustrate that rafting can be a means of range expansion over large distances, but may be insufficient for sustaining genetic connectivity across major barriers, thereby resulting in lineage divergence.

Estimating population parameters of longsnout seahorses, Hippocampus reidi (Teleostei: Syngnathidae) through mark-recapture

“…constant; (t) time-dependence; (g) group effect; (p=c) no recapture effect; (γ"= γ'=0) no emigration models; (γ"= γ') random emigration models; (γ" γ') Markovian emigration models. movements (Caldwell, Vincent, 2012;Boehm et al, 2013). These features were evident in our models suggesting constant and random patterns of temporary emigration.…”

“…Although we focused on quantifying population parameters in a population, its local dynamics is coupled with a broader-scale dynamic, being influenced by other mechanisms such as dispersal, climate variability and biological interactions (Bjørnstad et al, 1999). For instance, despite having small home ranges, being poor swimmers and being highly associated with the substrate, seahorses can perform long-distance dispersal by passively rafting in floating algal mats (Boehm et al, 2013). This passive dispersal might exert a strong influence in the meta-population dynamics of seahorse species.…”

Population assignment and local adaptation along an isolation‐by‐distance gradient in Pacific cod (Gadus macrocephalus)

“…The Amazon, Yangtze, and Mississippi River outflows, for example, limit cross‐barrier dispersal in corals, limpets ( Cellana toreuma ), seahorses ( Hippocampus spp. ), various reef fishes, red snapper ( Lutjanus campechanus ), and other organisms (Boehm et al., 2013; Dong et al., 2012; Potts, 1983). Yet, it must be noted that temporal structuring, which was not examined in this study, cannot be ruled out.…”

New records of Hippocampus patagonicus Piacentino & Luzzatto, 2004 (Teleostei: Syngnathidae) from the coast of Paraná, southern Brazil

“…The seahorse H. patagonicus seems to have a limited and uneven distribution in Brazil, known only from a few records from the states of Pernambuco, Rio de Janeiro, São Paulo, Paraná, Santa Catarina and Rio Grande do Sul (Anderson et al 2015, Silveira et al 2014; present study). Although it is well documented that seahorses, as a general rule, have high levels of site fidelity and small home ranges , the isolated and sparse populations of this species along the Brazilian coast might be consequence of long-distance migration, as described by Boehm et al (2013) and Luzzatto et al (2014). Regardless of their resilient bony structure, unique life history, and behavior of seahorses make them particularly vulnerable to habitat loss and overexploita tion .…”

“…Its distribution seems to be restricted to the coasts of Argentina and Brazil (Piacentino and Luzzatto 2004;Boehm et al 2013;González et al 2014;Silveira et al 2014), and this the southernmost occurring species of its genus in the Southwestern Atlantic Ocean. Previous records of H. patagonicus in Brazil were provided by Boehm et al (2013), Silveira et al (2014) and Anderson et al (2015).…”