Contrasting quantitative traits and neutral genetic markers for genetic resource assessment of Mesoamerican Cedrela odorata

We compared within-population variability and degree of population differentiation for neutral genetic markers (RAPDS) and eight quantitative traits in Central American populations of the endangered tree, Cedrela odorata. Whilst population genetic diversity for neutral markers (Shannon index) and quantitative traits (heritability, coefficient of additive genetic variation) were uncorrelated, both marker types revealed strong differentiation between populations from the Atlantic coast of Costa Rica and the rest of the species' distribution. The degree of interpopulation differentiation was higher for RAPD markers (F-ST 0.67 for the sampled Mesoamerican range) than for quantitative traits (Q(ST) = 0.30). Hence, the divergence in quantitative traits was lower than could have been achieved by genetic drift alone, suggesting that balancing selection for similar phenotypes in different populations of this species. Nevertheless, a comparison of pair-wise estimates of population differentiation in neutral genetic markers and quantitative traits revealed a strong positive correlation (r = 0.66) suggesting that, for C. odorata, neutral marker divergence could be used as a surrogate for adaptive gene divergence for conservation planning. The utility of this finding and suggested further work are discussed.

Mark-recapture may reveal more about ecology than about population trends: Demography of a threatened ghost bat (Macroderma gigas) population

Since European settlement in Australia, the geographical range of ghost bats (Macroderma gigas) has contracted northwards. Ghost bats are thought to occur in disjunct populations with little interpopulation migration, raising concerns over the current status and future viability of the southernmost colony, which has also been threatened by mining activity. To address these concerns, demographic parameters of the southernmost colony were estimated from a mark-recapture study conducted during 1975-1981. Female bats gave birth to a single young in late spring, but only 40% (22-70%, 95% CI) of females bred in their second year, increasing to 93% (87-97%, 95% CI) for females greater than or equal to 2 years old. Sixty-five percent of juveniles caught were female. Annual adult survival ranged between 0.57-0.77 for females and 0.43-0.66 for males, and was lowest over winter-spring and greatest in autumn-winter. Juvenile survival for the first year ranged between 0.35-0.46 for females and 0.29-0.42 for males. Adult survival varied among seasons, was negatively associated with rainfall, but was not associated with temperature beyond being lower in late winter. Poor survival may result from the inferior daytime roosts that bats must use if water seepage forces them to leave their normal roosts. Although these age-specific rates of fecundity and survival suggested a declining population, mark-recapture estimates of the population trend indicated stability over the study period. Counts at daytime roosts also suggested a population decline, but were considered unreliable because of an increasing tendency of bats to avoid detection. It is therefore likely that some assumptions in estimating survival were violated. These results provide a caution against the uncritical use of population projections derived from mark-recapture estimates of demographic parameters, and the use of untested indices as the basis for conservation decisions.

Estimates of sex- and age-class-specific survival probabilities for a southern Great Barrier Reef green sea turtle population

Sex- and age-class-specific survival probabilities of a southern Great Barrier Reef green sea turtle population were estimated using a capture - mark - recapture (CMR) study and a Cormack - Jolly - Seber (CJS) modelling approach. The CMR history profiles for 954 individual turtles tagged over a 9-year period ( 1984 - 1992) were classified into three age classes ( adult, subadult, juvenile) based on somatic growth and reproductive traits. Reduced-parameter CJS models, accounting for constant survival and time-specific recapture, fitted best for all age classes. There were no significant sex-specific differences in either survival or recapture probabilities for any age class. Mean annual adult survival was estimated at 0.9482 (95% CI: 0.92 - 0.98) and was significantly higher than survival for either subadults or juveniles. Mean annual subadult survival was 0.8474 ( 95% CI: 0.79 - 0.91), which was not significantly different from mean annual juvenile survival estimated at 0.8804 ( 95% CI: 0.84 - 0.93). The time-specific adult recapture probabilities were a function of sampling effort but this was not the case for either juveniles or subadults. The sampling effort effect was accounted for explicitly in the estimation of adult survival and recapture probabilities. These are the first comprehensive sex- and age-class-specific survival and recapture probability estimates for a green sea turtle population derived from a long-term CMR program.

Genetic resource impacts of habitat loss and degradation; reconciling empirical evidence and predicted theory for neotropical trees

The theoretical impacts of anthropogenic habitat degradation on genetic resources have been well articulated. Here we use a simulation approach to assess the magnitude of expected genetic change, and review 31 studies of 23 neotropical tree species to assess whether empirical case studies conform to theory. Major differences in the sensitivity of measures to detect the genetic health of degraded populations were obvious. Most studies employing genetic diversity (nine out of 13) found no significant consequences, yet most that assessed progeny inbreeding (six out of eight), reproductive output (seven out of 10) and fitness (all six) highlighted significant impacts. These observations are in line with theory, where inbreeding is observed immediately following impact, but genetic diversity is lost slowly over subsequent generations, which for trees may take decades. Studies also highlight the ecological, not just genetic, consequences of habitat degradation that can cause reduced seed set and progeny fitness. Unexpectedly, two studies examining pollen flow using paternity analysis highlight an extensive network of gene flow at smaller spatial scales (less than 10 km). Gene flow can thus mitigate against loss of genetic diversity and assist in long-term population viability, even in degraded landscapes. Unfortunately, the surveyed studies were too few and heterogeneous to examine concepts of population size thresholds and genetic resilience in relation to life history. Future suggested research priorities include undertaking integrated studies on a range of species in the same landscapes; better documentation of the extent and duration of impact; and most importantly, combining neutral marker, pollination dynamics, ecological consequences, and progeny fitness assessment within single studies.

Complex life cycles and offspring provisioning in marine invertebrates

Offspring size can have pervasive effects throughout an organism's life history. Mothers can make either a few large or many small offspring, and the balance between these extremes is determined by the relationship between offspring size and performance. This relationship in turn is thought to be determined by the offspring's environment. Recently, it has become clear that events in one life-history stage can strongly affect performance in another. Given these strong carryover effects, we asked whether events in the larval phase can change the relationship between offspring size and performance in the adult phase. We manipulated the length of the larval period in the bryozoan Bugula neritina and then examined the relationship between offspring size and various parameters of adult performance under field conditions. We found that despite the adult stage being outplanted into identical conditions, different offspring sizes were predicted to be optimal, depending on the experience of those adults as larvae. This work highlights the fact that the strong phenotypic links between life-history stages may result in optimal offspring size being highly unpredictable for organisms with complex life cycles.

Aspects of the biology of the yabby Trypea australiensis (Dana) (Decapoda : Thalassinidea) and the potential of burrow counts as an indirect measure of population density

The thalassinidean shrimp Trypea australiensis (the yabby) commonly occurs on intertidal sandflats and subtidal regions of sheltered embayments and estuaries along the east coast of Australia and is harvested commercially and recreationally for use as bait by anglers. The potential for counts of burrow openings to provide a reliable indirect estimate of the abundance of yabbies was examined on intertidal sandflats on North Stradbroke Island (Queensland, Australia). The relationship between the number of burrow openings and the abundance of yabbies was generally poor and also varied significantly through time, casting doubt on previous estimates of abundance for this species based on unvalidated hole counts. Spatial and temporal variation in population density, the size at maturity and the reproductive period of the yabby were also assessed. Except for an initial peak in abundance as a result of recruitment, the density of yabbies was constant throughout the study but considerably less than that estimated from a previous study in the same area. Ovigerous females were recorded at 3 mm carapace length (CL) which is smaller than previously recorded for this species and thalassinideans in general. Small ovigerous females were found throughout the study, including the summer months, which is unusual for thalassinideans in the intertidal zone. It was hypothesised that in the intertidal zone, small female yabbies may be able to balance the metabolic demands of reproduction and respiration at higher temperatures than can larger females allowing them to reproduce in the warmer months.

Genetic population structure of the catadromous perciform: Macquaria novemaculeata (Percichthyidae)

Genetic population structure in the catadromous Australian bass Macquaria novemaculeata was investigated using samples from four locations spanning 600 km along the eastern Australian coastline. Both allozymes and mtDNA control region sequences were examined. Population subdivision estimates based on allozymes revealed low levels of population structuring (G(st)=0.043, P<0.05). However, mtDNA indicated moderate levels of geographic population structure (G(st)=0.146, P<0.01). Phylogenetic analysis of mtDNA control region sequences (mean sequence divergence 1.9%) indicated little phylogeographic structuring. Results suggested that genotypic variation within each river population, while bring affected primarily by genetic drift, was also prevented from more significant divergence by homogenizing levels of gene flow-synonymous with a one-dimensional stepping-stone model of population structure. The catadromous life history of Macquaria novemaculeata was considered to br influential on the pattern of population structure displayed. Results were compared to the few population genetic studies involving catadromous fishes, indicating that catadromy alone is unlikely to be a good predictor of population structure. A more comprehensive suite of biological characteristics than simple life-history traits must be considered fully to allow reliable predictive models of population structure to be formulated. (C) 1997 The Fisheries Society of the British Isles.

Sex allocation in the sexually monomorphic fairy martin

Offspring sex ratios were examined at the population and family level in the sexually monomorphic, socially monogamous fairy martin Petrochelidon ariel at five colony sites over a 4-year period (1993 1996). The sex of 465 nestlings from 169 broods % as determined using sex-specific PCR at the CHD locus. In accordance with predicted sex allocation patterns, population sex ratios at hatching and fledging did not differ from parity in an), year and the variance in brood sex ratios did not deviate from the binomial distribution, Further, brood sex ratio did not vary with hatching date during the season, brood number, brood size or colony size, The sex ratio or broods with extra-pair young did not differ from those without, while the sex ratio of broods fathered by males that gained extra-pair fertilizations did not differ from broods fathered by other males. Extra-pair chicks were as likely to be male as female. Neither the total number of feeding visits to the brood nor the relative feeding contribution by the sexes varied significantly with brood sex ratio. Brood sex ratios were also unrelated to paternal size, condition and breeding experience or maternal condition and breeding experience, However, contrary to our prediction, brood sex ratio was negatively correlated with maternal size. Generally, these results were consistent with our expectations that brood sex ratios would not vary with environmental factors or parental characteristics, and would not influence the level of parental provisioning. However, the finding that females with longer tarsi produced an excess of daughters is difficult to reconcile with our current understanding or fairy martin life history and breeding ecology.

Biological determinants of extinction risk: why are smaller species less vulnerable?

It is becoming increasingly clear that species of smaller body size tend to be less vulnerable to contemporary extinction threats than larger species, but few studies have examined the mechanisms underlying this pattern. In this paper, data for the Australian terrestrial mammal fauna are used to ask whether higher reproductive output or smaller home ranges can explain the reduced extinction risk of smaller species. Extinct and endangered species do indeed have smaller litters and larger home ranges for their body size than expected under a null model. In multiple regressions, however, only litter size is a significant predictor of extinction risk once body size and phylogeny are controlled for. Larger litters contribute to fast population growth, and are probably part of the reason that smaller species are less extinction-prone. The effect of litter size varies between the mesic coastal regions and the and interior of Australia, indicating that the environment a species inhabits mediates the effect of biology on extinction risk. These results suggest that predicting extinction risk from biological traits is likely to be a complex task which must consider explicitly interactions between biology and environment.

Increase of a Caribbean leatherback turtle Dermochelys coriacea nesting population linked to long-term nest protection

The leatherback turtle Dermochelys coriacea is considered to be at serious risk of global extinction, despite ongoing conservation efforts. Intensive long-term monitoring of a leatherback nesting population on Sandy Point (St. Croix, US Virgin Islands) offers a unique opportunity to quantify basic population parameters and evaluate effectiveness of nesting beach conservation practices. We report a significant increase in the number of females nesting annually from ca. 18-30 in the 1980s to 186 in 2001, with a corresponding increase in annual hatchling production from ca. 2000 to over 49,000. We then analyzed resighting data from 1991 to 2001 with an open robust-design capture-mark-recapture model to estimate annual nester survival and adult abundance for this population. The expected annual survival probability was estimated at ca. 0.893 (95% CL 0.87-0.92) and the population was estimated to be increasing ca. 13% pa since the early 1990s. Taken together with DNA fingerprinting that identify mother-daughter relations, our findings suggest that the increase in the size of the nesting population since 1991 was probably due to an aggressive program of beach protection and egg relocation initiated more than 20 years ago. Beach protection and egg relocation provide a simple and effective conservation strategy for this Northern Caribbean nesting population as long as adult survival at sea remains relatively high. (c) 2005 Elsevier Ltd. All rights reserved.

Evaluating trends in abundance of immature green turtles, Chelonia mydas, in the Greater Caribbean

Many long-lived marine species exhibit life history traits. that make them more vulnerable to overexploitation. Accurate population trend analysis is essential for development and assessment of management plans for these species. However, because many of these species disperse over large geographic areas, have life stages inaccessible to human surveyors, and/or undergo complex developmental migrations, data on trends in abundance are often available for only one stage of the population, usually breeding adults. The green turtle (Chelonia mydas) is one of these long-lived species for which population trends are based almost exclusively on either numbers of females that emerge to nest or numbers of nests deposited each year on geographically restricted beaches. In this study, we generated estimates of annual abundance for juvenile green turtles at two foraging grounds in the Bahamas based on long-term capture-mark-recapture (CMR) studies at Union Creek (24 years) and Conception Creek (13 years), using a two-stage approach. First, we estimated recapture probabilities from CMR data using the Cormack-Jolly-Seber models in the software program MARK; second, we estimated annual abundance of green turtles. at both study sites using the recapture probabilities in a Horvitz-Thompson type estimation procedure. Green turtle abundance did not change significantly in Conception Creek, but, in Union Creek, green turtle abundance had successive phases of significant increase, significant decrease, and stability. These changes in abundance resulted from changes in immigration, not survival or emigration. The trends in abundance on the foraging grounds did not conform to the significantly increasing trend for the major nesting population at Tortuguero, Costa Rica. This disparity highlights the challenges of assessing population-wide trends of green turtles and other long-lived species. The best approach for monitoring population trends may be a combination of (1) extensive surveys to provide data for large-scale trends in relative population abundance, and (2) intensive surveys, using CMR techniques, to estimate absolute abundance and evaluate the demographic processes' driving the trends.

A framework for the study of genetic variation in migratory behaviour

Evolutionary change results from selection acting on genetic variation. For migration to be successful, many different aspects of an animal's physiology and behaviour need to function in a co-coordinated way. Changes in one migratory trait are therefore likely to be accompanied by changes in other migratory and life-history traits. At present, we have some knowledge of the pressures that operate at the various stages of migration, but we know very little about the extent of genetic variation in various aspects of the migratory syndrome. As a consequence, our ability to predict which species is capable of what kind of evolutionary change, and at which rate, is limited. Here, we review how our evolutionary understanding of migration may benefit from taking a quantitative-genetic approach and present a framework for studying the causes of phenotypic variation. We review past research, that has mainly studied single migratory traits in captive birds, and discuss how this work could be extended to study genetic variation in the wild and to account for genetic correlations and correlated selection. In the future, reaction-norm approaches may become very important, as they allow the study of genetic and environmental effects on phenotypic expression within a single framework, as well as of their interactions. We advocate making more use of repeated measurements on single individuals to study the causes of among-individual variation in the wild, as they are easier to obtain than data on relatives and can provide valuable information for identifying and selecting traits. This approach will be particularly informative if it involves systematic testing of individuals under different environmental conditions. We propose extending this research agenda by using optimality models to predict levels of variation and covariation among traits and constraints. This may help us to select traits in which we might expect genetic variation, and to identify the most informative environmental axes. We also recommend an expansion of the passerine model, as this model does not apply to birds, like geese, where cultural transmission of spatio-temporal information is an important determinant of migration patterns and their variation.

Costs and decisions in population management: Koalas on Kangaroo Island

Many populations have a negative impact on their habitat, or upon other species in the environment, if their numbers become too large. For this reason they are often managed using some form of control. The objective is to keep numbers at a sustainable level, while ensuring survival of the population.+Here we present models that allow population management programs to be assessed. Two common control regimes will be considered: reduction and suppression. Under the suppression regime the previous population is maintained close to a particular threshold through near continuous control, while under the reduction regime, control begins once the previous population reaches a certain threshold and continues until it falls below a lower pre-defined level. We discuss how to best choose the control parameters, and we provide tools that allow population managers to select reduction levels and control rates. Additional tools will be provided to assess the effect of different control regimes, in terms of population persistence and cost.In particular we consider the effects of each regime on the probability of extinction and the expected time to extinction, and compare the control methods in terms of the expected total cost of each regime over the life of the population. The usefulness of our results will be illustrated with reference to the control of a koala population inhabiting Kangaroo Island, Australia.