Mitochondrial DNA from the extinct dusky seaside sparrow (Ammodramus maritimus nigrescens) was compared in terms of nucleotide sequence divergence to mitochondrial DNAs from extant populations of seaside sparrows. Analyses of restriction sites revealed a close phylogenetic affinity of A. m. nigrescens to other sparrow populations along the Atlantic coast of the United States but considerable genetic distance from Gulf coast birds. Concerns and applied management strategies for the seaside sparrow have been based on a morphological taxonomy that does not adequately reflect evolutionary relationships within the complex.

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Nucleotide sequences from the cytochrome b gene of mitochondrial DNA were employed to resolve phylogenetic controversies and to assess molecular evolutionary rates in marine turtles (Chelonioidea) (mya), and by 150 mya fully marine forms made their appearance (1). However, the subsequent evolution of marine turtles has been a matter of much speculation and debate, as is reflected in uncertainties about evolutionary relationships at taxonomic levels ranging from subspecies to suborders (Table 1). Previous hypotheses regarding the phylogeny of marine turtles ( Fig. 1) have rested primarily on morphologic characters and a reasonably abundant fossil record. Here we provide an independent assessment of evolutionary relationships among all eight extant species, based on nucleotide sequences from the cytochrome b gene of mitochondrial DNA (mtDNA).One motivation for this study is to clarify marine turtle phylogeny in problematic areas that are relevant to the fields of both evolutionary ecology and conservation genetics (Table 1). For example, the molecular phylogeny is used to decipher the evolutionary origin of an unusual dietary habit of the hawksbill turtle, spongivory. Furthermore, all of the marine turtle species are formally listed by the International Union for the Conservation ofNature and Natural Resources as threatened or endangered, and by enhancing phylogenetic understanding, genetic information may influence strategies for allocating finite management resources. At present, several national and international conservation programs are directed toward various marine turtles whose relationships and even specific status are in question.A second rationale for this study is to evaluate recent suggestions of a significant slowdown in the evolutionary rate of turtle mtDNA relative to many other vertebrates (6-8).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

The Iceland population of Anguilla eels contains an elevated frequency of fish with vertebral numbers lower than those typical of European localities. Several distinct hypotheses have been advanced to account for these morphologically atypical fish: for example, they could represent (1) genetically "pure" American expatriates, (2) genetically "pure" European types with ontogenetic abnormalities, or (3) hybrids between American and European forms. Here we critically test these and other possibilities by examining the joint distributions of allozyme markers, mitochondrial DNA markers, and vertebral numbers in Icelandic eels. The particular patterns of association among the genetic and morphological traits demonstrate that the Iceland population includes, in low frequency, the products of hybridization between American and European eels. Approximately 2-4% of the gene pool in the Iceland eel population is derived from American eel ancestry. This hybrid zone is highly unusual in the biological world, because the mating events in catadromous eels presumably take place thousands of kilometers from where the hybrids are observed as maturing juveniles. The molecular data, in conjunction with the geographic distributions, strongly suggest that the differences in migrational behavior and morphology between American and European eels include an important additive genetic component. Evolutionary hypotheses are advanced to account for the original separation of North Atlantic eels into American and European populations, and for the presence of hybrids in Iceland.

Apparently monogamous animals often prove, upon genetic inspection, to mate polygamously. Seahorse males provide care in a brood pouch. An earlier genetic study of the Western Australian seahorse demonstrated that males mate with only one female for each particular brood. Here we investigate whether males remain monogamous in sequential pregnancies during a breeding season. In a natural population we tagged males and sampled young from two successive broods of 14 males. Microsatellite analyses of parentage revealed that eight males re‐mated with the same female, and six with a new female. Thus, in this first study to document long‐term genetic monogamy in a seahorse, we show that switches of mates still occur. Polygynous males moved greater distances between broods, and tended to have longer interbrood intervals, than monogamous males, suggesting substantial costs associated with the breaking of pair bonds which may explain the high degree of social monogamy in this fish genus.