William S. Nelson

Molecular genetic relationships of the extinct dusky seaside sparrow.

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.

Mitochondrial gene trees and the evolutionary relationship of Mallard and black ducks

We assayed restriction site differences in mitochondrial DNA (mtDNA) within and among allopatric populations of the Mallard (Anas platyrhynchos) and the American Black Duck (A. rubripes). The observed mtDNA clones grouped into two phylogenetically distinct arrays that we estimate differ by about 0.8% in nucleotide sequence. Genotypes in one clonal array were present in both species, while genotypes in the other array were seen only in Mallards. In terms of the mtDNA “gene tree,” the assayed Mallards exhibit a paraphyletic relationship with respect to Black Ducks, meaning that genealogical separations among some extant haplotypes in the Mallard predate the species separation. Evidence is advanced that this pattern probably resulted from demographically based processes of lineage sorting, rather than recent, secondary introgressive hybridization. However, haplotype frequencies were most similar among conspecific populations, so the Mallard and Black Ducks cluster separately in terms of a population phenogram. The results provide a clear example of the distinction between a gene tree and a population tree, and of the distinction between data analyses that view individuals versus populations as operational taxonomic units (OTUs). Overall, the mtDNA data indicate an extremely close evolutionary relationship between Mallards and Black Ducks, and in conjunction with the geographic distributions suggest that the Black Duck is a recent evolutionary derivative of a more broadly distributed Mallard‐Black ancestor.

MOLECULAR GENETIC DISSECTION OF SPAWNING, PARENTAGE, AND REPRODUCTIVE TACTICS IN A POPULATION OF REDBREAST SUNFISH, LEPOMIS AURITUS

Despite a great diversity of reproductive behaviors in fishes, few studies have examined the genetic consequences of alternative reproductive tactics. Here we develop and employ microsatellite markers to assess genetic paternity and maternity of progeny cohorts in a population of redbreast sunfish (Lepomis auritus), a species in which males build and tend nests. Nearly 1000 progeny from 25 nests, plus nest‐attendant males and nearby adults, were genotyped at microsatellite loci that displayed more than 18 alleles each. The genetic data demonstrate that multiple females (at least two to six) spawned in each nest, their offspring were spatially dispersed across a nest, and more than 90% of the young were sired by the attendant male. However, about 40% of the nests also showed genetic evidence of low‐level reproductive parasitism, and two nests were tended by males that had fathered none of the sampled offspring. Genetically deduced reproductive behaviors in this population of redbreast sunfish contrast with those reported previously in bluegill sunfish (L. macrochirus) wherein heteromorphic males specialized for parasitism or for parental care coexist in high frequency. Thus, nest‐parasitic reproductive behaviors in fishes appear to be evolutionary labile.

Genetic monogamy and biparental care in an externally fertilizing fish, the largemouth bass (Micropterus salmoides).

Breeding, male North American sunfish (Centrarchidae), are often brightly coloured and promiscuous. However, the largemouth bass (Micropterus salmoides) is sexually monomorphic in appearance and socially monogamous. Unlike some other nest–tending centrarchids in the genus Lepomis, largemouth bass have also been reported to provide biparental care to eggs and fry. Here we use microsatellite markers in order to test whether social monogamy predicts genetic monogamy in the largemouth bass. Offspring were collected from 26 nests each usually guarded by a pair of adults, many of which were also captured. Twenty–three of these progeny cohorts (88%) proved to be composed almost exclusively of full–sibs and were thus the product of monogamous matings. Cuckoldry by males was rare. The genetic data also revealed that some nests contain juveniles that were not the progeny of the guardian female, a finding that can be thought of as low–level ‘female cuckoldry’. Overall, however, the data provide what may be the first genetic documentation of near–monogamy and biparental care in a vertebrate with external fertilization.

Phylogeography of colonially nesting seabirds, with special reference to global matrilineal patterns in the sooty tern (Sterna fuscata).

Sooty tern (Sterna fuscata) rookeries are scattered throughout the tropical oceans. When not nesting, individuals wander great distances across open seas, but, like many other seabirds, they tend to be site‐faithful to nesting locales in successive years. Here we examine the matrilineal history of sooty terns on a global scale. Assayed colonies within an ocean are poorly differentiated in mitochondrial DNA sequence, a result indicating tight historical ties. However, a shallow genealogical partition distinguishes Atlantic from Indo‐Pacific rookeries. Phylogeographic patterns in the sooty tern are compared to those in other colonially nesting seabirds, as well as in the green turtle (Chelonia mydas), an analogue of tropical seabirds in some salient aspects of natural history. Phylogeographic structure within an ocean is normally weak in seabirds, unlike the pronounced matrilineal structure in green turtles. However, the phylogeographic partition between Atlantic and Indo‐Pacific rookeries in sooty terns mirrors, albeit in shallower evolutionary time, the major matrilineal subdivision in green turtles. Thus, global geology has apparently influenced historical gene movements in these two circumtropical species.

Molecular Documentation of Polyembryony and the Micro-Spatial Dispersion of Clonal Sibships in the Nine-Banded Armadillo, Dasypus novemcinctus

A battery of allelic markers at highly polymorphic microsatellite loci was developed and employed to confirm, genetically, the clonal nature of sibships in nine-banded armadillos. This phenomenon of consistent polyembryony, otherwise nearly unknown among the vertebrates, was capitalized upon to describe the micro-spatial distributions of numerous clonal sibships in a natural population of armadillos. Adult clone mates were significantly more dispersed than were juvenile sibs, suggesting limited opportunities for altruistic behavioural interactions among mature individuals. These results, and considerations of armadillo natural history, suggest that evolutionary explanations for polyembryony in this species may not reside in the kinds of ecological and kin selection theories relevant to some of the polyembryonic invertebrates. Rather, polyembryony in armadillos may be associated evolutionarily with other reproductive peculiarities of the species, including delayed uterine implantation of a single egg.

Genetic maternity and paternity in a local population of armadillos assessed by microsatellite DNA markers and field data.

Genetic data from polymorphic microsatellite loci were employed to estimate paternity and maternity in a local population of nine‐banded armadillos (IDasypus novemcinctus) in northern Florida. The parentage assessments took advantage of maximum likelihood procedures developed expressly for situations when individuals of neither gender can be excluded a priori as candidate parents. The molecular data for 290 individuals, interpreted alone and in conjunction with detailed biological and spatial information for the population, demonstrate high exclusion probabilities and reasonably strong likelihoods of genetic parentage assignment in many cases; low mean probabilities of successful reproductive contribution to the local population by individual armadillo adults in a given year; and statistically significant microspatial associations of parents and their offspring. Results suggest that molecular assays of highly polymorphic genetic systems can add considerable power to assessments of biological parentage in natural populations even when neither parent is otherwise known.

Mitochondrial DNA Phylogeography and Subspecies Issues in the Monotypic Freshwater Turtle Sternotherus odoratus

Phylogeographic variation in mitochondrial (mt) DNA restriction sites is described for populations of the monotypic stinkpot turtle (Sternotherus odoratus) from the southeastern United States. Stinkpots display pronounced and hierarchical mtDNA phylogeographic differentiation, ranging from genetically shallow differences among local populations to genetically deep distinctions among regional assemblages of haplotypes. Both magnitude and general pattern of intraspecific mtDNA phylogeography in S. odoratus are remarkably similar to those in a related species (Sternotherus minor) that traditionally has been considered ditypic based on morphological and genetic appraisals. The pronounced phylogeographic population structure in S. odoratus effectively falsifies prior hypotheses that extensive dispersal and gene flow account for the morphometric conservatism among geographic populations. These findings also raise broader issues concerning the significance of subspecies designations in testudine systematics.

Development and application of long-PCR for the assay of full-length animal mitochondrial DNA.

Keywords: polymerase chain reaction; molecular evolution; DNA amplification; restriction fragment length polymorphisms

Matrilineal history of the endangered Cape Sable seaside sparrow inferred from mitochondrial DNA polymorphism.

Restriction analyses were conducted on mitochondrial DNA (mtDNA) amplified by long‐PCR from an endangered bird, the Cape Sable seaside sparrow. The first of several successful mtDNA amplifications was accomplished using the partially digested tissue remains of a transmitter‐monitored bird retrieved from the gut of a snake. As many as 91 mtDNA restriction fragments produced by 18 endonucleases were compared in this and four other Cape Sable specimens against mtDNA similarly amplified by long‐PCR from other taxonomic forms in the seaside sparrow complex. Results indicate that the Cape Sable birds belong to an ‘Atlantic’ matrilineal clade, and are highly divergent from other seaside sparrows along the Gulf of Mexico.