Aim To evaluate the impact of a proposed ancient suture zone in the Gulf of Mexico on the distribution and molecular diversity of dispersal‐limited, sand‐burrowing amphipods of the genera Haustorius and Lepidactylus (Haustoriidae: Amphipoda). Location Gulf of Mexico, USA and Mexico. Methods Phylogenetic and population genetic analyses were performed using mitochondrial (COI and 16S) and nuclear (18S and 28S) data from 93 amphipod individuals from 16 sites across the Gulf of Mexico. Bayesian and ML phylogenies were constructed for all genes, divergence times were estimated using a molecular clock for COI (0.007–0.013 subs./site per Myr), and four species delimitation methods were used to identify operational taxonomic units (OTUs) within each amphipod species. The mitochondrial COI gene was used to construct haplotype networks and estimate population genetic parameters to evaluate historical changes in effective population sizes. Results Deep divergences (most estimated to be >4 Ma) were uncovered between sister clades of both amphipod genera on either side of the Mississippi River as well as within Lepidactylus triarticulatus where each sample site was found to harbour a unique genetic lineage. Two cryptic OTUs of L. triarticulatus were identified living sympatrically at Pass Christian, Mississippi. Two distinct OTUs representing western and eastern Haustorius galvezi clades were identified along the Texas and Mexico coastlines with abutting ranges. Population genetic results show some support for recent population expansions for western Gulf OTUs, while eastern Gulf OTUs may have suffered population bottlenecks in the past. Main conclusions Divergences between sister species of sand‐burrowing amphipods exceeds the timing of previous vicariant hypotheses. The split appears to be consistent with Miocene sedimentation levels from the Mississippi River acting as an east–west barrier to gene flow in the Gulf of Mexico. Given their strong population structure and cryptic diversity, haustoriid amphipods are ideal model organisms for studying open coast biogeography.
Undescribed species of the genus Haustorius Müller, 1775 have long been known to exist in the Gulf of Mexico. These sand-burrowing amphipods are abundant intertidal members of fine sand beaches. Two new species are here described, Haustorius galvezi sp. nov. and Haustorius allardi sp. nov. The range of H. jayneae is extended to Carrabelle Beach, FL. A review of the genera Haustorius and Lepidactylus is included, as well as notes on their ecology and biogeography. Additionally, a full key to all known Haustoriidae of the Gulf of Mexico is presented.
The Modern Synthesis (or “Neo‐Darwinism”), which arose out of the reconciliation of Darwin's theory of natural selection and Mendel's research on genetics, remains the foundation of evolutionary theory. However, since its inception, it has been a lightning rod for criticism, which has ranged from minor quibbles to complete dismissal. Among the most famous of the critics was Stephen Jay Gould, who, in 1980, proclaimed that the Modern Synthesis was “effectively dead.” Gould and others claimed that the action of natural selection on random mutations was insufficient on its own to explain patterns of macroevolutionary diversity and divergence, and that new processes were required to explain findings from the fossil record. In 1982, Charlesworth, Lande, and Slatkin published a response to this critique in Evolution, in which they argued that Neo‐Darwinism was indeed sufficient to explain macroevolutionary patterns. In this Perspective for the 75th Anniversary of the Society for the Study of Evolution, we review Charlesworth et al. in its historical context and provide modern support for their arguments. We emphasize the importance of microevolutionary processes in the study of macroevolutionary patterns. Ultimately, we conclude that punctuated equilibrium did not represent a major revolution in evolutionary biology – although debate on this point stimulated significant research and furthered the field – and that Neo‐Darwinism is alive and well.
Species range contractions both contribute to, and result from, biological annihilation, yet do not receive the same attention as extinctions. Range contractions can lead to marked impacts on populations but are usually characterized only by reduction in extent of range. For effective conservation, it is critical to recognize that not all range contractions are the same. We propose three distinct patterns of range contraction: shrinkage, amputation, and fragmentation. We tested the impact of these patterns on populations of a generalist species using forward-time simulations. All three patterns caused 86–88% reduction in population abundance and significantly increased average relatedness, with differing patterns in declines of nucleotide diversity relative to the contraction pattern. The fragmentation pattern resulted in the strongest effects on post-contraction genetic diversity and structure. Defining and quantifying range contraction patterns and their consequences for Earth’s biodiversity would provide useful and necessary information to combat biological annihilation.
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