Post-Glacial Expansion and Population Genetic Divergence of Mangrove Species Avicennia germinans (L.) Stearn and Rhizophora mangle L. along the Mexican Coast

Abstract

Mangrove forests in the Gulf of California, Mexico represent the northernmost populations along the Pacific coast and thus they are likely to be source populations for colonization at higher latitudes as climate becomes more favorable. Today, these populations are relatively small and fragmented and prior research has indicated that they are poor in genetic diversity. Here we set out to investigate whether the low diversity in this region was a result of recent colonization, or fragmentation and genetic drift of once more extensive mangroves due to climatic changes in the recent past. By sampling the two major mangrove species, Rhizophora mangle and Avicennia germinans, along the Pacific and Atlantic coasts of Mexico, we set out to test whether concordant genetic signals could elucidate recent evolution of the ecosystem. Genetic diversity of both mangrove species showed a decreasing trend toward northern latitudes along the Pacific coast. The lowest levels of genetic diversity were found at the range limits around the Gulf of California and the outer Baja California peninsula. Lack of a strong spatial genetic structure in this area and recent northern gene flow in A. germinans suggest recent colonization by this species. On the other hand, lack of a signal of recent northern dispersal in R. mangle, despite the higher dispersal capability of this species, indicates a longer presence of populations, at least in the southern Gulf of California. We suggest that the longer history, together with higher genetic diversity of R. mangle at the range limits, likely provides a gene pool better able to colonize northwards under climate change than A. germinans.

Genetic Diversity of the Black Mangrove Avicennia germinans (L.) Stearn in Northwestern Mexico

“…Overall, genetic diversity was relatively low, consistent with previous reports for northern East-Pacific mangrove populations [35,36]. No significant differences were observed in genetic diversity among preserved and perturbed sites in the analyzed generations (adults and saplings).…”

Is the central‐marginal hypothesis a general rule? Evidence from three distributions of an expanding mangrove species, Avicennia germinans (L.) L

“…CMH predictions are supported along multiple mangrove distributions controlled by either temperature or precipitation (Arnaud‐Haond et al, ; De Ryck et al, ; Francisco, Mori, Alves, Tambarussi, & de Souza, ; Kennedy et al, ; Maguire, Saenger, Baverstock, & Henry, ; Pil et al, ; Sugai et al, ), consistent with our findings along temperature‐controlled Florida. CMH is also supported in Pacific Mexico (Ochoa‐Zavala et al, ; Sandoval‐Castro et al, , ) and Western Australia (Arnaud‐Haond et al, ; Binks et al, ), where parallel declines in temperature and precipitation limit mangrove distributions. Our finding that CMH is not supported across TX‐LA seems to be an exception to the general rule in mangroves, although the Middle East may also prove to be an exception as the entire region is precipitation limited (Osland, Feher, et al, ).…”

Selfing ability and drift load evolve with range expansion

“…; Sandoval‐Castro et al. ; however see Petit ). In C. americana , declines in effective population size are relatively modest and of uniform magnitude across geographic space.…”