Caitlin Curtis

Genetic Diversity Despite Population Collapse in a Critically Endangered Marine Fish: The Smalltooth Sawfish (Pristis pectinata)

Sawfish (family Pristidae) are among the most critically endangered marine fish in the world, yet very little is known about how genetic bottlenecks, genetic drift, and inbreeding depression may be affecting these elasmobranchs. In the US Atlantic, the smalltooth sawfish (Pristis pectinata) has declined to 1-5% of its abundance in the 1900s, and its core distribution has contracted to southwest Florida. We used 8 polymorphic microsatellite markers to show that this remnant population still exhibits high genetic diversity in terms of average allelic richness (18.23), average alleles per locus (18.75, standard deviation [SD] 6.6) and observed heterozygosity (0.43-0.98). Inbreeding is rare (mean individual internal relatedness = -0.02, SD 0.14; F(IS) = -0.011, 95% confidence interval [CI] = -0.039 to 0.011), even though the estimated effective population size (N(e)) is modest (250-350, 95% CI = 142-955). Simulations suggest that the remnant smalltooth sawfish population will probably retain >90% of its current genetic diversity over the next century even at the lower estimate of N(e). There is no evidence of a genetic bottleneck accompanying last centurys demographic bottleneck, and we discuss hypotheses that could explain this. We also discuss features of elasmobranch life history and population biology that could make them less vulnerable than other large marine vertebrates to genetic change associated with reduced population size.

Pleistocene population expansions of Antarctic seals

We sequenced a portion (c. 475 bp) of the mitochondrial control region of three species of Antarctic phocid carnivores (Weddell seal, Leptonychotes weddellii, N = 181; crabeater seal, Lobodon carcinophaga, N = 143; and Ross seal, Ommatophoca rossii, N = 41) that live seasonally or permanently in the fast ice and seasonal pack ice of the western Amundsen and Ross seas of western Antarctica. We resolved 251 haplotypes with a haplotype diversity of 0.98 to 0.99. Bayesian estimates of Θ from the program LAMARC ranged from 0.075 for Weddell seals to 0.576 for crabeater seals. We used the values of theta to estimate female effective population sizes (NEF), which were 40 700 to 63 000 for Weddell seals, 44 400 to 97 800 for Ross seals, and 358 500 to 531 900 for crabeater seals. We used mismatch distributions to test for historical population size expansions. Weddell seals and crabeater seals had significant, unimodal mean pairwise difference distributions (P = 0.56 and 0.36, respectively), suggesting that their populations expanded suddenly around 731 000 years ago (Weddell seals) and around 1.6 million years ago (crabeater seals). Both of these expansions occurred during times of intensified glaciations and may have been fostered by expanding pack ice habitat.

DNA fingerprinting in zoology: past, present, future.

In 1962, Thomas Kuhn famously argued that the progress of scientific knowledge results from periodic ‘paradigm shifts’ during a period of crisis in which new ideas dramatically change the status quo. Although this is generally true, Alec Jeffreys’ identification of hypervariable repeat motifs in the human beta-globin gene, and the subsequent development of a technology known now as ‘DNA fingerprinting’, also resulted in a dramatic shift in the life sciences, particularly in ecology, evolutionary biology, and forensics. The variation Jeffreys recognized has been used to identify individuals from tissue samples of not just humans, but also of many animal species. In addition, the technology has been used to determine the sex of individuals, as well as paternity/maternity and close kinship. We review a broad range of such studies involving a wide diversity of animal species. For individual researchers, Jeffreys’ invention resulted in many ecologists and evolutionary biologists being given the opportunity to develop skills in molecular biology to augment their whole organism focus. Few developments in science, even among the subsequent genome discoveries of the 21st century, have the same wide-reaching significance. Even the later development of PCR-based genotyping of individuals using microsatellite repeats sequences, and their use in determining multiple paternity, is conceptually rooted in Alec Jeffreys’ pioneering work.

Fifty-nine microsatellite markers for hybrid classification studies involving endemic Florida Mottled Duck (Anas fulvigula fulvigula) and invasive Mallards (A. platyrhynchos)

Endemic Florida Mottled Duck (Anas fulvigula fulvigula) appear to be hybridizing introgressively with domesticated Mallards (A. platyrhynchos), which are frequently released or escape captivity and have established feral populations throughout Florida. To investigate this possible conservation threat, we isolated and characterized 59 polymorphic loci from an enriched Florida Mottled Duck microsatellite library and performed cross-amplification assays with Mallard specimens. Average numbers of alleles per locus were 6.0 (ranging 2–23) and 5.6 (ranging 2–15) for A. fulvigula and A. platyrhynchos, respectively; estimates of observed/expected heterozygosity were 0.54/0.63 and 0.52/0.64. Markers developed in this study will be used in conjunction with existing markers to robustly classify hybrids and to assess and monitor the genetic dynamics of introgression between these waterfowl species.

Long-term site fidelity of endangered smalltooth sawfish (Pristis pectinata) from different mothers

Understanding how endangered species use nursery habitats is vital for recovery planning. Research on the smalltooth sawfish (Pristis pectinata) has shown that areas of estuarine nurseries, called hotspots, are used consistently. The objectives of our study were 1) to determine whether 10 young-of-the-year smalltooth sawfish in an artificial, non-main-stem portion (i.e., a seawall canal system) of a hotspot were descended from one or different mothers and 2) to document long-term habitat use by these individuals. At least 4 mothers contributed to the group, which comprised siblings, half-siblings, and unrelated individuals. Young sawfish exhibited site fidelity to their capture location, spending 61% of their time there. Continuous residency lasted as long as 86 days, but these fish made small-scale diel (< 1 river km) movements between the capture location (day) and the nearby main-riverstem portion of the hotspot (night). Larger-scale (5-7 river km) downriver and upriver relocations between the capture location and the river mouth, including 2 other known natural hotspots, occurred after a tropical storm. This research shows that 1) young-of-the-year from different mothers can have high site fidelity at specific locations within a nursery hotspot and 2) these hotspots can be important for young-of-the-year even when there is a drastic change in freshwater inflow.