Showing papers by "John C. Avise published in 2003"

Sympatric speciation as a consequence of male pregnancy in seahorses.

Abstract: The phenomenon of male pregnancy in the family Syngnathidae (seahorses, pipefishes, and sea dragons) undeniably has sculpted the course of behavioral evolution in these fishes. Here we explore another potentially important but previously unrecognized consequence of male pregnancy: a predisposition for sympatric speciation. We present microsatellite data on genetic parentage that show that seahorses mate size-assortatively in nature. We then develop a quantitative genetic model based on these empirical findings to demonstrate that sympatric speciation indeed can occur under this mating regime in response to weak disruptive selection on body size. We also evaluate phylogenetic evidence bearing on sympatric speciation by asking whether tiny seahorse species are sister taxa to large sympatric relatives. Overall, our results indicate that sympatric speciation is a plausible mechanism for the diversification of seahorses, and that assortative mating (in this case as a result of male parental care) may warrant broader attention in the speciation process for some other taxonomic groups as well.

Microsatellite Variation and Differentiation in North Atlantic Eels

Abstract: We screened 11 populations of American, European, and Icelandic eels (Anguillidae) for allelic variation and genetic divergence at six polymorphic microsatellite loci. Within either of the two recognized Anguilla species in the North Atlantic (rostrata in the Americas, anguilla in Europe), population genetic structure was statistically significant but weak; fully 95% of the total genetic variation was present within geographic locales rather than distributed among them. The two Anguilla species also overlap greatly in allelic frequencies, so the available data proved ineffective for addressing hypotheses about the possible hybrid origins of some Icelandic eels. The overlapping microsatellite profiles contrast with nearly diagnostic species differences documented previously in allozymes and mtDNA. This and similar empirical findings in several other species support theoretical concerns that homoplasy (convergent evolution) in allelic states can compromise the utility of rapidly mutating microsatellite loci for certain types of microevolutionary questions regarding gene flow and species differences.

Catadromous Eels of the North Atlantic: A Review of Molecular Genetic Findings Relevant to Natural History, Population Structure, Speciation, and Phylogeny

Abstract: The North Atlantic is home to two recognized species of “freshwatereels” (Fig. 1): Anguilla Rostrata of the Americas, and A. anguilla of Europe and North Africa. Like the approximately 13 other named Anguilla species of the western Indo-Pacific region (Ege 1939; Jellyman 1987; Nelson 1994), Atlanticeels have a catadromous life cycle, spending most of their lives in estuarine or inland waters, but, on reaching sexual maturity, migrating far out to sea for a once-in-a-lifetime (semelparous) spawn (Bertin 1957; Tesch 1977; but see also Tsukamoto et al. 1998). This peculiar life history has raised a number of interesting ecological and evolutionary questions. Does spawning byeels in the open sea occur at random with respect to the coastal localities from which the adults had emigrated? Does the dispersal of larvae back to North America and Europe occur in ways that genetically homogenize continental populations across vast geographic areas? How does speciation occur within the context of this diadromous life cycle? Do different morphological forms of Atlanticeels hybridize? How and when dideels colonize the Atlantic from their probable ancestral homeland in the Indo-Pacific? This review examines how molecular genetic data from polymorphic markers have contributed to a current understanding of the natural history and evolution of Atlanticeels.

The Best and the Worst of Times for Evolutionary Biology

Abstract: The 21st century will offer great opportunities, but also challenges, for the field of evolutionary biology, particularly in areas related to molecular genetic technologies, the environment, biodiversity, and public education. The coming decades promise to be both the best and the worst of times for the evolutionary disciplines.