Genetic structure of the southeastern United States loggerhead turtle nesting aggregation: evidence of additional structure within the peninsular Florida recovery unit

The southeastern United States supports one of two large loggerhead turtle (Caretta caretta) nesting aggregations worldwide and is therefore critical to global conservation and recovery efforts for the species. Previous studies have established the presence of four demographically distinct nesting populations (management units) corresponding to beaches from (1) North Carolina through northeastern Florida, (2) peninsular Florida, (3) the Dry Tortugas, and (4) northwest Florida. Temporal and geographic genetic structure of the nesting aggregation was examined utilizing partial mitochondrial control region haplotype frequencies from 834 samples collected over the 2002 through 2008 nesting seasons from 19 beaches as well as previously published haplotype data. Most rookeries did not exhibit interannual genetic variation. However, the interannual variation detected did significantly impact the interpretation of spatial genetic structure in northeastern Florida. Based on pairwise F _ST comparisons, exact tests of population differentiation, and analysis of molecular variance, the present study upholds the distinctiveness of the four currently recognized management units and further supports recognition of discrete central eastern, southern (southeastern and southwestern), and central western Florida management units. Further subdivision may be warranted, but more intensive genetic sampling is required. In addition, tools such as telemetry and mark-recapture are needed to complement genetic data and overcome limitations of genetic markers in resolving loggerhead turtle rookery connectivity in the southeastern USA.     

Effects of life‐history requirements on the distribution of a threatened reptile

Survival and reproduction are the two primary life‐history traits essential for species’ persistence; however, the environmental conditions that support each of these traits may not be the same. Despite this, reproductive requirements are seldom considered when estimating species’ potential distributions. We sought to examine potentially limiting environmental factors influencing the distribution of an oviparous reptile of conservation concern with respect to the species’ survival and reproduction and to assess the implications of the species’ predicted climatic constraints on current conservation practices. We used ecological niche modeling to predict the probability of environmental suitability for the alligator snapping turtle (Macrochelys temminckii). We built an annual climate model to examine survival and a nesting climate model to examine reproduction. We combined incubation temperature requirements, products of modeled soil temperature data, and our estimated distributions to determine whether embryonic development constrained the northern distribution of the species. Low annual precipitation constrained the western distribution of alligator snapping turtles, whereas the northern distribution was constrained by thermal requirements during embryonic development. Only a portion of the geographic range predicted to have a high probability of suitability for alligator snapping turtle survival was estimated to be capable of supporting successful embryonic development. Historic occurrence records suggest adult alligator snapping turtles can survive in regions with colder climes than those associated with consistent and successful production of offspring. Estimated egg‐incubation requirements indicated that current reintroductions at the northern edge of the species’ range are within reproductively viable environmental conditions. Our results highlight the importance of considering survival and reproduction when estimating species’ ecological niches, implicating conservation plans, and benefits of incorporating physiological data when evaluating species’ distributions.     

Twenty-Six Years of Green Turtle Nesting at Tortuguero, Costa Rica: An Encouraging Trend

The green turtle ( Chelonia mydas ) population that nests at Tortuguero, Costa Rica, is the largest in the Atlantic by at least an order of magnitude. Surveys to monitor the nesting activity on the northern 18 km of the 36-km beach were initiated in 1971 and extended to the entire beach in 1986. From the survey data, we estimated the total number of nesting emergences on the northern 18 km for each year from 1971 through 1996. Evaluation of the trend in nesting emergences indicated a relatively consistent increase from 1971 to the mid-1980s, constant or perhaps decreasing nesting during the late 1980s, and then resumption of an upward trend in the 1990s. Evaluation of trends in sea turtle nesting populations requires many years of data because of the large degree of annual variation in nesting numbers. The trends reported in this study must be evaluated with caution for several reasons. First, if the mean number of nests deposited by each female each year (clutch frequency) varies significantly among years, changes in the number of nesting emergences among years could reflect changes in the number of nesting females, clutch frequency, or both. Second, we only assessed the trend in one segment of the population (mature females), which may or may not represent the trend of the entire green turtle population and which, because of late maturity, may not reflect changes in juvenile mortality for many years. Third, survey frequency, and thus confidence in annual estimates, varied among years. The upward population trend must be assessed from the perspective of the catastrophic decline that the Caribbean green turtle populations have experienced since the arrival of Europeans. If careful management is continued in Costa Rica and adopted throughout the region, the collapse of the Caribbean green turtle populations—which seemed imminent in the 1950s—can be avoided.     

Hidden demographic impacts of fishing and environmental drivers of fecundity in a sea turtle population

Fisheries bycatch is a critical threat to sea turtle populations worldwide, particularly because turtles are vulnerable to multiple gear types. The Canary Current is an intensely fished region, yet there has been no demographic assessment integrating bycatch and population management information of the globally significant Cabo Verde loggerhead turtle (Caretta caretta) population. Using Boa Vista island (Eastern Cabo Verde) subpopulation data from capture–recapture and nest monitoring (2013–2019), we evaluated population viability and estimated regional bycatch rates (2016–2020) in longline, trawl, purse-seine, and artisanal fisheries. We further evaluated current nesting trends in the context of bycatch estimates, existing hatchery conservation measures, and environmental (net primary productivity) variability in turtle foraging grounds. We projected that current bycatch mortality rates would lead to the near extinction of the Boa Vista subpopulation. Bycatch reduction in longline fisheries and all fisheries combined would increase finite population growth rate by 1.76% and 1.95%, respectively. Hatchery conservation increased hatchling production and reduced extinction risk, but alone it could not achieve population growth. Short-term increases in nest counts (2013–2021), putatively driven by temporary increases in net primary productivity, may be masking ongoing long-term population declines. When fecundity was linked to net primary productivity, our hindcast models simultaneously predicted these opposing long-term and short-term trends. Consequently, our results showed conservation management must diversify from land-based management. The masking effect we found has broad-reaching implications for monitoring sea turtle populations worldwide, demonstrating the importance of directly estimating adult survival and that nest counts might inadequately reflect underlying population trends.     

Genetic and Demographic Threats to the Black Rhinoceros Population in the Ngorongoro Crater

A resident population of 13 black rhinoceros ( Diceros bicornis ) persist in Ngorongoro Crater, Tanzania. The effective population size ( N _e ) may be as few as 5 animals. Projected growth for this population suggests that the effective population size will remain small for the near future, threatening this Iocal population with extinction due to the stochastic factors associated with small population size. A summary of historic and recent demographic data for this population reveals a population crash during the period of heavy poaching that affected this species throughout its range. Although poaching of this species has been brought under control the population remains small. These data and models of projected population growth argue for consideration of more-intensive management within the framework of the small population paradigm. This case is an example of applied conservation resulting from this paradigm used in conjunction with rather than competing with the declining population paradigm. We identify additional monitoring, particularly of density-dependent behaviors, that will be necessary for designing a successful management program. Finally, the use of molecular markers for developing an accurate pedigree for this population is suggested in order to maintain a genetically healthy population. These strategies have broad applicability to black rhinoceros conservation throughout Africa.     

Putting Longline Bycatch of Sea Turtles into Perspective

Abstract:  Although some sea turtle populations are showing encouraging signs of recovery, others continue to decline. Reversing population declines requires an understanding of the primary factor(s) that underlie this persistent demographic trend. The list of putative factors includes direct turtle and egg harvest, egg predation, loss or degradation of nesting beach habitat, fisheries bycatch, pollution, and large-scale changes in oceanographic conditions and nutrient availability. Recently, fisheries bycatch, in particular bycatch from longline fisheries, has received increased attention and has been proposed as a primary source of turtle mortality. We reviewed the existing data on the relative impact of longline bycatch on sea turtle populations. Although bycatch rates from individual longline vessels are extremely low, the amount of gear deployed by longline vessels suggests that cumulative bycatch of turtles from older age classes is substantial. Current estimates suggest that even if pelagic longlines are not the largest single source of fisheries-related mortality, longline bycatch is high enough to warrant management actions in all fleets that encounter sea turtles. Nevertheless, preliminary data also suggest that bycatch from gillnets and trawl fisheries is equally high or higher than longline bycatch with far higher mortality rates. Until gillnet and trawl fisheries are subject to the same level of scrutiny given to pelagic longlines, our understanding of the overall impact of fisheries bycatch on vulnerable sea turtle populations will be incomplete.     

Cause-specific temporal and spatial trends in green sea turtle strandings in the Hawaiian Archipelago (1982–2003)

We investigated cause-specific temporal and spatial trends in sea turtle strandings in the Hawaiian Archipelago. Five species of sea turtle were recorded in 3,861 strandings over a 22-year period (1982–2003). Green turtles comprised 97% of these strandings with size and gender composition reflecting the demographic structure of the resident green turtle population and relative green turtle abundance in Hawaiian waters. The cause of strandings was determined by necropsy based on a complete gross external and internal examination. Totally 75% of the 3,732 green turtle strandings were from Oahu where strandings occur year-round. The most common known cause of the green turtle strandings was the tumour-forming disease, fibropapillomatosis (28%) followed by hook-and-line fishing gear-induced trauma (7%), gillnet fishing gear-induced trauma (5%), boat strike (2.5%), and shark attack (2.7%). Miscellaneous causes comprised 5.4% of strandings whereas 49% of green turtle strandings could not be attributed to any known cause. Green turtle strandings attributable to boat strike were more likely from Kauai and Oahu while fibropapilloma strandings were more likely from Oahu and Maui. Hook-and-line gear strandings were more likely from Oahu due to higher per capita inshore fishing effort. The specific mortality rate (conditional probability) for fibropapillomatosis was 88%, 69% for gillnet gear and 52% for hook-and-line gear. The probability of a dead green turtle stranding increased from 1982 but levelled off by the mid-1990s. The declining mortality risk was because the prevalence and severity of fibropapillomatosis has decreased recently and so has the mortality risk attributable to gillnet gear. Despite exposure to disease and inshore fishing gears, the Hawaiian green turtle stock continues to recover following protection since the late 1970s. Nevertheless, measures to reduce incidental capture of sea turtles in coastal Hawaiian fisheries would be prudent, especially since strandings attributable to hook-and-line fishing gear have increased steadily since 1982.     

Survival and remigration probabilities for loggerhead turtles (Caretta caretta) nesting in the eastern Gulf of Mexico

Few long-term mark-recapture tagging datasets exist to estimate population parameters for loggerhead sea turtle (Caretta caretta) recovery units. Using a two-state open robust design model, we analyzed a 20-year (1990–2009) mark-recapture dataset from the Keewaydin Island loggerhead nesting assemblage off the southwest coast of Florida (USA) in the eastern Gulf of Mexico. For this analysis, 2,292 turtle encounters were evaluated, representing 841 individual nesting turtles. Survival was estimated at 0.73 (95 % CI 0.69–0.76). This estimate is comparable with survival estimates elsewhere in the Peninsular Florida subpopulation and is among the lowest estimates for the Northwest Atlantic loggerhead population. We documented no changes in remigration rates or clutch frequency over time. These are the first survival and remigration probabilities estimated for a loggerhead nesting assemblage in the eastern Gulf of Mexico.     

Estimating freshwater turtle mortality rates and population declines following hook ingestion

Freshwater turtle populations are susceptible to declines following small increases in the mortality of adults, making it essential to identify and understand potential threats. Freshwater turtles ingest fish hooks associated with recreational angling, and this is likely a problem because hook ingestion is a source of additive mortality for sea turtles. We used a Bayesian‐modeling framework, observed rates of hook ingestion by freshwater turtles, and mortality of sea turtles from hook ingestion to examine the probability that a freshwater turtle in a given population ingests a hook and subsequently dies from it. We used the results of these analyses and previously published life‐history data to simulate the effects of hook ingestion on population growth for 3 species of freshwater turtle. In our simulation, the probability that an individual turtle ingests a hook and dies as a result was 1.2–11%. Our simulation results suggest that this rate of mortality from hook ingestion is sufficient to cause population declines. We believe we have identified fish‐hook ingestion as a serious yet generally overlooked threat to the viability of freshwater turtle populations.     

Spatio-temporal patterns of juvenile marine turtle occurrence in waters of the European continental shelf

We present data spanning approximately 100 years regarding the spatial and temporal occurrence of marine turtle sightings and strandings in the northeast Atlantic from two public recording schemes and demonstrate potential signals of changing population status. Records of loggerhead (n = 317) and Kemp’s ridley (n = 44) turtles occurring on the European continental shelf were most prevalent during the autumn and winter, when waters were coolest. In contrast, endothermic leatherback turtles (n = 1,668) were most common during the summer. Analysis of the spatial distribution of hard-shell marine turtle sightings and strandings highlights a pattern of decreasing records with increasing latitude. The spatial distribution of sighting and stranding records indicates that arrival in waters of the European continental shelf is most likely driven by North Atlantic current systems. Future patterns of spatial-temporal distribution, gathered from the periphery of juvenile marine turtles habitat range, may allow for a broader assessment of the future impacts of global climate change on species range and population size.     

Incorporating multidimensional behavior into a risk management tool for a critically endangered and migratory species

Conservation of migratory species exhibiting wide-ranging and multidimensional behaviors is challenged by management efforts that only utilize horizontal movements or produce static spatial–temporal products. For the deep-diving, critically endangered eastern Pacific leatherback turtle, tools that predict where turtles have high risks of fisheries interactions are urgently needed to prevent further population decline. We incorporated horizontal–vertical movement model results with spatial–temporal kernel density estimates and threat data (gear-specific fishing) to develop monthly maps of spatial risk. Specifically, we applied multistate hidden Markov models to a biotelemetry data set (n = 28 leatherback tracks, 2004–2007). Tracks with dive information were used to characterize turtle behavior as belonging to 1 of 3 states (transiting, residential with mixed diving, and residential with deep diving). Recent fishing effort data from Global Fishing Watch were integrated with predicted behaviors and monthly space-use estimates to create maps of relative risk of turtle–fisheries interactions. Drifting (pelagic) longline fishing gear had the highest average monthly fishing effort in the study region, and risk indices showed this gear to also have the greatest potential for high-risk interactions with turtles in a residential, deep-diving behavioral state. Monthly relative risk surfaces for all gears and behaviors were added to South Pacific TurtleWatch (SPTW) ( https://www.upwell.org/sptw ), a dynamic management tool for this leatherback population. These modifications will refine SPTW's capability to provide important predictions of potential high-risk bycatch areas for turtles undertaking specific behaviors. Our results demonstrate how multidimensional movement data, spatial–temporal density estimates, and threat data can be used to create a unique conservation tool. These methods serve as a framework for incorporating behavior into similar tools for other aquatic, aerial, and terrestrial taxa with multidimensional movement behaviors.     

Genetic structure of green turtle (Chelonia mydas) peripheral populations nesting in the northwestern Pacific rookeries: evidence for northern refugia and postglacial colonization

Several green turtle (Chelonia mydas) nesting populations have been reported in the northwestern Pacific region, the northernmost limit of its distribution range. However, the population history in this region as a whole is not well understood. To clarify how the green turtle nesting populations have evolved in the northwestern Pacific region, the genetic composition of mitochondrial DNA control region sequences in the northwestern Pacific was compared with that of the other Pacific populations. We analyzed 302 samples from the northwestern Pacific rookeries, including 78 newly collected samples from rookeries in the Ryukyu Archipelago, Japan (from 24.27°N, 123.76°E to 28.45°N, 129.61°E). Our results revealed that the northwestern Pacific populations consisted of one highly endemic lineage (Clade IV) in the northwestern Pacific rookeries and two other lineages (Clades I and V) which were widely observed in other Pacific populations. We concluded that the highly endemic lineage indicated that a refugial population existed in this region during the Last Glacial Maximum, and the other two lineages indicated that colonization from populations at lower latitudes occurred during interglacial periods. The green turtle nesting populations in the present periphery of their distribution range had been thought to have their origin in colonization from lower latitudes, which served as refugia during glacial periods. However, the present results indicated that the northwestern Pacific peripheral populations have been maintained on the evolutionary timescale of this species and should be treated as long-term conservation resources.     

Incorporating Uncertainty of Management Costs in Sensitivity Analyses of Matrix Population Models

The importance of accounting for economic costs when making environmental‐management decisions subject to resource constraints has been increasingly recognized in recent years. In contrast, uncertainty associated with such costs has often been ignored. We developed a method, on the basis of economic theory, that accounts for the uncertainty in population‐management decisions. We considered the case where, rather than taking fixed values, model parameters are random variables that represent the situation when parameters are not precisely known. Hence, the outcome is not precisely known either. Instead of maximizing the expected outcome, we maximized the probability of obtaining an outcome above a threshold of acceptability. We derived explicit analytical expressions for the optimal allocation and its associated probability, as a function of the threshold of acceptability, where the model parameters were distributed according to normal and uniform distributions. To illustrate our approach we revisited a previous study that incorporated cost‐efficiency analyses in management decisions that were based on perturbation analyses of matrix population models. Incorporating derivations from this study into our framework, we extended the model to address potential uncertainties. We then applied these results to 2 case studies: management of a Koala (Phascolarctos cinereus) population and conservation of an olive ridley sea turtle (Lepidochelys olivacea) population. For low aspirations, that is, when the threshold of acceptability is relatively low, the optimal strategy was obtained by diversifying the allocation of funds. Conversely, for high aspirations, the budget was directed toward management actions with the highest potential effect on the population. The exact optimal allocation was sensitive to the choice of uncertainty model. Our results highlight the importance of accounting for uncertainty when making decisions and suggest that more effort should be placed on understanding the distributional characteristics of such uncertainty. Our approach provides a tool to improve decision making.     

Variation in adult annual survival probability and remigration intervals of sea turtles

We analyzed a large dataset to quantify adult annual survival probability and remigration intervals for the Tortuguero, Costa Rica green turtle population. Annual survival probability was estimated at 0.85 (95% CI 0.75–0.92) using a recovery model and at 0.85 (95% CI 0.83–0.87) using an open robust design model. The two most common modes of remigration are 2 and 3 years. Annual survival probability is lower and remigration intervals are shorter than for other green turtle populations. Explanations for short remigration intervals include reproductive compensation due to historic population declines, availability of better quality food items, favorable environmental conditions, and short distance to the main foraging grounds. Variation in survival and remigration intervals have profound consequences for management and life history evolution. The short remigration intervals of Tortuguero green turtles partly offset mortality caused by turtle fishing in Nicaragua and mean that low juvenile survival represents a more urgent threat to the population than low adult survival. Low adult survival probability could result in selective pressure for earlier age at maturity.     

Spatial and temporal variability in somatic growth of green sea turtles (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) resident in the Hawaiian Archipelago

The somatic growth dynamics of green turtles (Chelonia mydas) resident in five separate foraging grounds within the Hawaiian Archipelago were assessed using a robust non-parametric regression modelling approach. The foraging grounds range from coral reef habitats at the north-western end of the archipelago, to coastal habitats around the main islands at the south-eastern end of the archipelago. Pelagic juveniles recruit to these neritic foraging grounds from ca. 35 cm SCL or 5 kg (~6 years of age), but grow at foraging-ground-specific rates, which results in quite different size- and age-specific growth rate functions. Growth rates were estimated for the five populations as change in straight carapace length (cm SCL year^–1) and, for two of the populations, also as change in body mass (kg year^–1). Expected growth rates varied from ca. 0–2.5 cm SCL year^–1, depending on the foraging-ground population, which is indicative of slow growth and decades to sexual maturity, since expected size of first-time nesters is 80 cm SCL. The expected size-specific growth rate functions for four populations sampled in the south-eastern archipelago displayed a non-monotonic function, with an immature growth spurt at ca. 50–53 cm SCL (~18–23 kg) or ca. 13–19 years of age. The growth spurt for the Midway atoll population in the north-western archipelago occurs at a much larger size (ca. 65 cm SCL or 36 kg), because of slower immature growth rates that might be due to a limited food stock and cooler sea surface temperature. Expected age-at-maturity was estimated to be ca. 35–40 years for the four populations sampled at the south-eastern end of the archipelago, but it might well be >50 years for the Midway population. The Hawaiian stock comprises mainly the same mtDNA haplotype, with no differences in mtDNA stock composition between foraging-ground populations, so that the geographic variability in somatic growth rates within the archipelago is more likely due to local environmental factors rather than genetic factors. Significant temporal variability was also evident, with expected growth rates declining over the last 10–20 years, while green turtle abundance within the archipelago has increased significantly since the mid-1970s. This inverse relationship between somatic growth rates and population abundance suggests a density-dependent effect on somatic growth dynamics that has also been reported recently for a Caribbean green turtle stock. The Hawaiian green turtle stock is characterised by slow growth rates displaying significant spatial and temporal variation and an immature growth spurt. This is consistent with similar findings for a Great Barrier Reef green turtle stock that also comprises many foraging-ground populations spanning a wide geographic range.Communicated by P.W. Sammarco, Chauvin     

Evolutionary Significant Units versus Geopolitical Taxonomy: Molecular Systematics of an Endangered Sea Turtle (genus Chelonia)

Abstract: Taxonomic rank is an important criterion in assessing the conservation priority of an endangered organism: the sole member of a distinct family will generally receive a higher priority than a semi-isolated population in a polytypic species. When cryptic evolutionary partitions are discovered in endangered species, these findings are heralded as a positive step in the conservation process. The opposite action, demoting the taxonomic rank of an endangered organism, can be resisted by the conservation community because it is perceived as detrimental to preservation efforts. We explore the arguments for and against the species status of the endangered black turtle ( Chelonia agassizii ) and contribute an additional data set based on DNA sequences of single-copy nuclear loci. These data are concordant with previous mtDNA surveys in indicating no evolutionary distinction between C. agassizii and adjacent green turtle ( C. mydas ) populations. Although the black turtle is morphologically identifiable at a low level, much of its distinction is based on size and color differences that are highly variable throughout the range of C. mydas . Thus the black turtle would be more accurately classified at the subspecific or population level. There is no strong scientific case available to defend the species status of C. agassizii , and yet that designation has persisted for over a century. We suggest that the maintenance of this name is based on geographical and political considerations, and we propose a pragmatic category for this type of taxonomy: the geopolitical species . Furthermore, we argue against the practice of preserving species status for conservation purposes. There are several good reasons to preserve the black turtle, including morphological diversity and the possibility that it is an incipient evolutionary lineage with novel adaptations; taxonomic rank, however, is not one of them.     

Importance of Assessing Population Genetic Structure before Eradication of Invasive Species: Examples from Insular Norway Rat Populations

Abstract:  Determining the inter-island migration abilities of pest species and delimiting eradication units enable more viable long-term eradication campaigns because recurrent colonization from neighboring islands is avoided. We examined the genetic structure of the invasive Norway rat ( Rattus norvegicus ) to identify gene flow between islands and delimit population units at different geographical scales. We investigated variation in eight microsatellite loci in rat populations from 18 islands, representing five archipelagos off the Brittany coast (France). Although most of the islands are isolated from each other, short genetic distances, weak F_ST values between close islands, and a high level of cross-assignment showed that individuals collected on different islands could represent a single population unit. A Bayesian clustering method also supported the existence of high levels of gene flow between some neighboring islands. Thus, the statement "one island equals one population" can be false when inter-island distances are less than a few hundred meters. Genetic studies enable the definition of island clusters among which migration may occur that should be considered eradication units. To avoid reinvasion and to minimize ecological and economic costs, rats on all islands in an eradication unit should be eradicated simultaneously. We suggest that the genetic monitoring we performed here can be applied for management of any pest.     

Evaluation of the Contribution of Genetic Research to the Management of the Endangered Plant Zieria prostrata

Abstract: Zieria prostrata (Rutaceae) is known from only four headlands within a 3-km stretch of coastline in New South Wales, Australia. The species was presumed to have occurred at a headland 24 km south of its present range. We used random amplified polymorphic DNA analysis to assess patterns of genetic variation within and among the extant populations. The analysis also included an individual reputedly rescued from the now extinct population. A high level of population divergence was revealed by principal coordinate analysis and an analysis of molecular variance (AMOVA; 37% among populations). Our genetic findings provide implications for the conservation management of the species. First, the loss of any one population would lead to a severe loss of genetic variation. Second, an adequate ex situ collection must sample the full range of genetic diversity from all populations. Third, the consequences of mixing populations may be an important conservation consideration if further translocations proceed. Fourth, the individual apparently sampled prior to its population extinction is genetically similar to individuals from one of the extant sites. This degree of similarity was unexpected and, after further investigation, led to the conclusion that prior existence of the species at the site is doubtful. Subsequently, a planned reintroduction program was abandoned. So far, of these four management implications, only the last has had a direct management outcome. Those implications that failed to lead to practical management outcomes did so because the same management recommendations could be obtained without genetic research. Clearly, the challenge for more effective conservation is to identify those cases in which genetic studies are likely to produce practical outcomes for conservation managers. This may be best achieved by assessing the outcomes of genetic studies already conducted.     

Critique of the Evolutionarily Significant Unit as a Definition for "Distinct Population Segments" under the U.S. Endangered Species Act

The U.S. Endangered Species Act grants protection to species, subspecies, and "distinct population segments" of vertebrate species. Historically, Congress included distinct population segments into endangered species legislation to enable the U.S. Fish and Wildlife Service to implement a flexible and pragmatic approach in listing populations of vertebrate species. Recently, the U.S. Fish and Wildlife Service and the National Marine Fisheries Service have proposed a policy that would narrowly define distinct population segments as evolutionarily significant units based on morphological and genetic distinctiveness between populations. Historically, the power to list species or populations as distinct population segments has been used to tailor management practices to unique circumstances; grant varied levels of protection in different parts of a species' range; protect species from extinction in significant portions of their ranges as well as to protect populations that are unique evolutionary entities. A strict redefinition of distinct population segments as evolutionarily significant units will compromise management efforts because the role of demographic and behavioral data will be reduced. Furthermore, strictly cultural, economic, or geographic justifications for listing populations as threatened or endangered will be greatly curtailed.     

DNA Fingerprinting Reveals a Lack of Genetic Variation in Northern Populations of the Western Pond Turtle (Clemmys marmorata)

I used DNA fingerprinting to provide the first analysis of the genetic composition of western pond turtle ( Clemmys marmorata ) populations in Washington, Oregon, and California. Populations of the western pond turtle in Washington and northern Oregon are rapidly approaching extinction. Genetic similarity within the largest northern populations, which are located inland, is high. An analysis of population substructure (F_st) revealed significant genetic divergence between inland populations, indicating a lack of dispersal and gene flow between sites. In contrast, northern coastal sites are not genetically distinct, but there are few if any viable populations remaining in this region. Genetic variability within southern California populations is a great deal higher than in northern inland sites. Similarly, a low F_st value indicated a lack of genetic differentiation between southern sites. An inter-regional analysis of population substructure (F_st = 0.24) revealed a significant degree of genetic divergence between geographical regions throughout the range. In addition, an estimate of western pond turtle phylogeny showed a genetic break in the species between northern and southern populations. Both population subdivision and phylogenetic analyses suggest a lack of appreciable gene flow between geographical regions for a considerable period of time. Genetic analyses support traditional subdivision based solely on the morphological variation of Clemmys marmorata into two subspecies: northern Clemmys marmorata marmorata and southern Clemmys marmorata pallida . Recovery of dwindling northern populations must combine demographic and genetic considerations. A first step should be to preserve local gene pools while augmenting population numbers, with the goal of preventing the extinction of this genetically and morphologically distinct subspecies.