Truncatus Populations Research Articles

Near‐shore distribution and abundance of dolphins along the West Coast of the South Island, New Zealand

Compared to other stretches of the New Zealand coast, very little is known about the cetacean fauna off the West Coast of the South Island. The purpose of this paper is to describe the near‐shore distribution and abundance of dolphins in that area by summarising the results of two major studies. Between February 1995 and February 1997, 97 day trips were undertaken from Westport, Greymouth, and Jackson Bay in a small boat to survey the near‐shore distribution of dolphins. Between July 1994 and February 1997, 283 field days were spent on the water in Doubtful Sound studying the local bottlenose dolphin (Tursiops truncatus) population of c. 63 individuals. At the same time, three longer surveys were undertaken into other fiords of Fiordland which indicated the presence of further populations. Altogether, five delphinid species were recorded in various abundances. Small‐medium‐sized groups of Hector's dolphins (Cephalorhynchus hectori) with 1–60 individuals were observed in almost all areas of Westland in winter as well as in summer. Maximum densities peaked at 5–18 individuals per nautical mile of coastline between Cape Foulwind and Hokitika. Dusky and common dolphins (Lagenorhynchus obscurus and Delphinus delphis) occurred almost exclusively in summer in groups of 2–150 individuals, often with calves, especially at Cape Foulwind and Jackson Head. Bottlenose dolphins (Tursiops truncatus) and killer whales (Orcinus orca) were observed rarely off Westland, but occurred more frequently in Fiordland.

Simulation Model of Prostephanus truncatus (Coleoptera: Bostrichidae) in Rural Maize Stores in the Republic of Benin

A distributed-delay, demographic simulation model of Prostephanus truncatus (Horn) populations in rural maize ( Zea mays L.) stores was developed and validated. Developmental and mortality parameters for eggs, larvae, and pupae, and the life span and fecundity data for adult insects, were estimated from published data and from laboratory experiments. The overall phenology of the simulated beetle dynamics reflected that of field data, although the model output tended to overestimate beetle population growth during the season and overall density late in the season. The model was developed as part of a low-cost tool for evaluating the major factors influencing population dynamics of stored-product pests and their natural enemies and to provide a conceptual framework for evaluating different control strategies in an integrated control context.

THE INFLUENCE OF SELF-FERTILIZATION AND POPULATION DYNAMICS ON THE GENETIC STRUCTURE OF SUBDIVIDED POPULATIONS: A CASE STUDY USING MICROSATELLITE MARKERS IN THE FRESHWATER SNAIL BULINUS TRUNCATUS.

The distribution of neutral genetic variability within and among sets of populations results from the combined actions of genetic drift, migration, extinction and recolonization processes, mutation, and the mating system. We here analyzed these factors in 38 populations of the hermaphroditic snail Bulinus truncatus. The sampling area covered a large part of the species range. The variability was analyzed using four polymorphic microsatellite loci. A very large number of alleles (up to 55) was found at the level of the whole study. Observed heterozygote deficiencies within populations are consistent with very high selfing rates, generally above 0.80, in all populations. These should depress the variability within populations, because of low effective size, genetic hitchhiking, and background selection, whatever the model of mutation assumed. However, that some populations exhibit much more variability than others suggests that historical demographic processes (e.g., population size variation, bottlenecks, or founding events) may play a significant role. A hierarchical analysis of the distribution of the variability across populations indicates a strong pattern of isolation by distance, whatever the geographical scale considered. Our analysis also illustrates how the mutation rate may affect population differentiation, as different mutation rates result in different levels of homoplasy at microsatellite loci. The effects of both genetic drift and gene flow vary with the temporal and spatial scales considered in B. truncatus populations.

INBREEDING DEPRESSION, NEUTRAL POLYMORPHISM, AND COPULATORY BEHAVIOR IN FRESHWATER SNAILS: A SELF-FERTILIZATION SYNDROME.

This paper examines the consequences of self-fertilization on life-history traits and neutral genetic polymorphism in natural populations of three species of hermaphrodite freshwater snails: Biomphalaria straminea, Bulinus globosus, and the aphallic species Bulinus truncatus. Life-history traits (fecundity, growth, hatching rate, and survival of offspring) are compared under laboratory conditions between isolated (obligatory selfing) and paired (outcrossing possible) snails in one population of B. straminea and B. globosus and two populations of B. truncatus. The genetic polymorphism of the same four populations is analyzed using electrophoretic markers in B. straminea and B. globosus and microsatellite markers in B. truncatus. In B. truncatus and B. straminea, isolated snails have a higher fecundity than paired snails, whereas the contrary is observed in B. globosus. For all populations, no difference in hatching rate and offspring survival is detected between the two treatments. Genetic analyses using microsatellite markers conducted in B. truncatus on progeny of paired snails reveal a high selfing rate in spite of high copulation rates, highlighting the difficulties of obtaining outcrossing in highly selfing snails. The high survival of selfed offspring in B. truncatus and B. straminea indicates that inbreeding depression is limited. The extent of inbreeding depression in B. globosus is less clear. Overall, fitness decrease in this species is limited to fecundity. The extent of allozyme polymorphism is very limited whereas a much higher variability is observed with microsatellites. Biomphalaria straminea and B. truncatus populations are also characterized by very low observed heterozygosities and large heterozygote deficiencies, whereas the B. globosus population does not exhibit such a deficiency. Overall these results allow the definition of a self-fertilization syndrome in hermaphrodite freshwater snails: selfing populations (such as those of B. straminea and B. truncatus studied here) are characterized by high selfing rates in spite of copulations, limited deleterious effects of selfing, limited neutral genetic polymorphism, and large heterozygote deficiencies.

Genetic variation in the bottlenose dolphinTursiops truncatusalong the KwaZulu/Natal coast, South Africa

Genetic variability and differentiation of the bottlenose dolphin Tursiops truncatus population along the KwaZulu/Natal coast was examined by horizontal starch gel electrophoresis. In all, 19 loci, encoding 14 allozymes, were resolved for 40 specimens. Three loci (15,8%) were polymorphic. Average heterozygosity for the population corresponded with values determined for other delphinid populations. However, the heterozygous state of the enzyme G6PD was only found in female bottlenose dolphins, suggesting that this enzyme may be X-linked in delphinids. Cluster analysis indicated a trend towards a north-south dichotomy in the KwaZulu/Natal population, a result supported by previously reported pollutant data as well as greater variability and smaller genetic distances in the southern cluster. However, non-significant FST values implied a lack of true genetic structure in the KwaZulu/Natal population. It is proposed that the annual influx of bottlenose dolphins from the Eastern Cape coast, in response to the migration of pilchard Sardinops sagax, results in the capture of dolphins "resident" on the KwaZulu/Natal south coast as well as Eastern Cape "migrants". Genetic variation between two potentially distinct populations may contribute to the elevated variability in the "resident" dolphins and the weak structuring of the KwaZulu/Natal population. Small sample sizes did not permit the evaluation of structure between "preferred areas" within KwaZulu/Natal.

Growth, Sexual Maturity and Food-Intake of Australian Indian-Ocean Bottle-Nosed Dolphins, Tursiops-Truncatus, in Captivity

Body size and food intake of four female and three male captive Indian Ocean bottlenose dolphins, Tursiops truncatus, were recorded regularly over a 10-year period. Growth of three captive-born female calves was also recorded. Growth of females parallelled that of South African bottlenose dolphins, tending toward an asymptote of c. 240 cm at 16 years of age. Growth of males was characterised by a secondary growth spurt at puberty between the ages of 10 and 12 years. Wild-caught females were approximately 10% heavier for age than their South African conspecifics. The captive-born females were up to 50% heavier than their African counterparts. Growth rates of females and males were 2.1-2.6 cm per year and 2.0-2.6 cm per year, respectively, between the ages of 3 and 16 years. Females were known to be reproductively mature at 11-13 years of age when lengths were between 227 and 238 cm. DNA fingerprinting of offspring and potential parents revealed that one of the three males was reproductively mature at 233 cm and another at either 222 or 226 cm. One of the males was sexually mature at the beginning of its secondary growth spurt at 10 or 11 years of age. Food intake of dolphins increased significantly with decreasing water temperature. It is suggested that variations in water temperature and food availability may play a role in governing body-size differences between T. truncatus populations.