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Eggs were sampled from 22 wild American alligator nests from the Rockefeller Wildlife Refuge in south-west Louisiana, along with the females guarding the nests. Three nests were sampled in 1995 and 19 were sampled in 1997. Females and offspring from all clutches were genotyped using five polymorphic microsatellite loci and the three nests from 1995 were also genotyped using one allozyme locus. Genotypes of the hatchlings were consistent with the guarding females being the mothers of their respective clutches. Multiple paternity was found in seven of the 22 clutches with one being fathered by three males, and the remaining six clutches having genotypes consistent with two males per clutch. Paternal contributions of multiply sired clutches were skewed. Some males sired hatchlings of more than one of the 22 clutches either as one of two sires of a multiple paternity clutch, as the sole sire of two different clutches, or as the sole sire of one clutch and one of two sires of a multiply sired clutch. There was no significant difference between females that had multiple paternity clutches and those that had singly sired clutches with respect to female total length (P = 0.844) and clutch size (P = 0.861). Also, there was no significant correlation between genetic relatedness of nesting females and pairwise nest distances (r2 = 0.003, F1,208 = 0.623, P = 0.431), indicating that females in this sample that nested close to one another were no more related than any two nesting females chosen at random. Eleven mutations were detected among hatchlings at the five loci over the 22 clutches. Most of these mutations (eight of 11) occurred at Ami(mu)-17, the only compound microsatellite locus of the five used in this study, corresponding to a mutation rate of 1.7 x 10-3. Finally, most of the mutations (82%) were homoplasious, i.e., mutating to an allelic state already present in this Louisiana population.

Microsatellites are short tandem arrays of simple DNA sequences, having a basic repeat unit of 1-5 bp (Tautz and Schlbtterer 1994). Microsatellite loci are abundant in most complex genomes (Tautz and Schlötterer 1994) and are usually highly polymorphic when the basic repeat unit is duplicated more than 10 times (Weber 1990). Alíeles at a locus differ in length due to variation in the number of repeats, and slipped strand mispairing is considered to be the major mechanism by which length variants (new alíeles) are generated (Levinson and Gutman 1987; Strand et al. 1993). Variation at microsatellite loci can be assayed by PCR amplification using primers complementary to unique sequences flanking specific repetitive arrays, followed by electrophoretic sizing of the PCR products (Tautz 1989). Because microsatellites are highly polymorphic and amenable to PCR, multiplex PCR, and automated scoring, they often are the molecular genetic marker of choice (e.g., Bruford and Wayne 1993). Although microsatellites occur in all eukaryotes (Tautz and Schlotteret 1994), their distribution and overall fi^equency varies widely (e.g., Langercrantz, Ellegren, and Andersson 1993). Because primer development can be time-consuming and costly, many investigators attempt to use primers developed in one species to amplify orthologous loci in closely related species (e.g., Moore et al. 1991). Some of these studies show that this strategy can be quite successfiil, even in distantly related species (e.g., FitzSimmons, Moritz, and Moore 1995). Most such cross-species comparisons, however, have tested either a small number of primer pairs (e.g., FitzSimmons, Moritz, and Moore 1995) or a small number of taxa (e.g., Moore et al. 1991). Additionally, only loci that are polymorphic in the species from which they are developed are used in most studies. The selection and use of such loci biases cross-taxa comparisons (Ellegren, Primmer, and Sheldon 1995). In general, primers that exhibit low levels of variation, as well as those that yield complex or unclear patterns, are discarded without much investigation or hesitation. Thus, it is not known how a reasonably large random sample of microsatellite sequences evolves within a group of taxa. We have developed primers to amplify microsatellite loci from American alligators (Alligator mississippiensis).

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have long been interested in the scientific research being conducted in their neighborhood, reflecting their concerns for nature and the future of their land. Bill Sr. has donated significant specimens to scientific collections, and all of the Millers have assisted our research in the Southwest in important ways. In addition, we thank them for good advice, several rescues, and much hospitality. Our work and our lives have been enriched and improved by our association with the Millers. 4 NO. 246 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY