Identifying environmental correlates of intraspecific genetic variation.

Genetic variation is critical to the persistence of populations and their capacity to adapt to environmental change. The distribution of genetic variation across a species' range can reveal critical information that is not necessarily represented in species occurrence or abundance patterns. We identified environmental factors associated with the amount of intraspecific, individual-based genetic variation across the range of a widespread freshwater fish species, the Murray cod Maccullochella peelii. We used two different approaches to statistically quantify the relative importance of predictor variables, allowing for nonlinear relationships: a random forest model and a Bayesian approach. The latter also accounted for population history. Both approaches identified associations between homozygosity by locus and both disturbance to the natural flow regime and mean annual flow. Homozygosity by locus was negatively associated with disturbance to the natural flow regime, suggesting that river reaches with more disturbed flow regimes may support larger, more genetically diverse populations. Our findings are consistent with the hypothesis that artificially induced perennial flows in regulated channels may provide greater and more consistent habitat and reduce the frequency of population bottlenecks that can occur frequently under the highly variable and unpredictable natural flow regime of the system. Although extensive river regulation across eastern Australia has not had an overall positive effect on Murray cod numbers over the past century, regulation may not represent the primary threat to Murray cod survival. Instead, pressures other than flow regulation may be more critical to the persistence of Murray cod (for example, reduced frequency of large floods, overfishing and chemical pollution).

Use of a microsatellite-based pedigree in estimation of heritabilities for economic traits in Australian blue mussel, Mytilus galloprovincialis.

This study aimed to estimate the heritabilities of three economically important traits (total weight, shell shape and meat yield) in Australian blue mussels. The estimates were derived using a pedigree reconstructed from a suite of both published and newly developed microsatellite markers. A total of 135 microsatellite loci were tested, of which 10 loci produced consistent PCR amplification and reliable results across all samples (74 full-sibling families including 74 pairs of parents and 2536 offspring). Lack of polymorphism at the non-repetitive region of the adhesive protein gene confirmed that the broodstock were derived from a single species. A total of 1538 progenies (62.5%) could be assigned to single parent pairs, and the remainder were assigned to two families or more, so were discarded from further analysis. Heritabilities for total weight, shell shape and meat yield were low (0.051 ± 0.027, 0.085 ± 0.038 and 0.049 ± 0.028, respectively) but reflected large environmental variation rather than limited genetic variation, suggesting a family-based breeding programme could improve these traits. The genetic correlation between weight and meat yield, expressed as percentage of total mussel which was not shell, was negative, while the genetic correlation between meat yield and shell shape was weakly positive.

Variable stocking effect and endemic population genetic structure in Murray cod Maccullochella peelii.

Microsatellite markers were utilized to examine the genetic structure of Murray cod Maccullochella peelii throughout its distribution in the Murray--Darling Basin (MDB) of eastern Australia, and to assess the genetic effects of over three decades of stocking hatchery-reared fingerlings. Bayesian analysis using the programme Structure indicated that the species is largely genetically panmictic throughout much of its extensive range, most probably due to the high level of connectivity between catchments. Three catchments with terminal wetlands (the Lachlan, Macquarie and Gwydir), however, contained genetically distinct populations. No stocking effects were detected in the catchments that were genetically panmictic (either because of low genetic power or lack of effects), but the genetically differentiated Gwydir and Macquarie catchment populations were clearly affected by stocking. Conversely, there was no genetic evidence for survival and reproduction of stocked fish in the Lachlan catchment. Therefore, stocking of M. peelii throughout the MDB has resulted in a range of genetic effects ranging from minimal detectable effect, to substantial change in wild population genetic structure.

Factorial aerobic scope is independent of temperature and primarily modulated by heart rate in exercising Murray cod (Maccullochella peelii peelii).

Several previous reports, often from studies utilising heavily instrumented animals, have indicated that for teleosts, the increase in cardiac output (Vb) during exercise is mainly the result of an increase in cardiac stroke volume (V(S)) rather than in heart rate (fH). More recently, this contention has been questioned following studies on animals carrying less instrumentation, though the debate continues. In an attempt to shed more light on the situation, we examined the heart rates and oxygen consumption rates (Mo2; normalised to a mass of 1 kg, given as Mo2kg) of six Murray cod (Maccullochella peelii peelii; mean mass+/-SE = 1.81+/-0.14 kg) equipped with implanted fH and body temperature data loggers. Data were determined during exposure to varying temperatures and swimming speeds to encompass the majority of the biological scope of this species. An increase in body temperature (Tb) from 14 degrees C to 29 degrees C resulted in linear increases in Mo2kg (26.67-41.78 micromol min(-1) kg(-1)) and fH (22.3-60.8 beats min(-1)) during routine exercise but a decrease in the oxygen pulse (the amount of oxygen extracted per heartbeat; 1.28-0.74 micromol beat(-1) kg(-1)). During maximum exercise, the factorial increase in Mo2kg was calculated to be 3.7 at all temperatures and was the result of temperature-independent 2.2- and 1.7-fold increases in fH and oxygen pulse, respectively. The constant factorial increases in fH and oxygen pulse suggest that the cardiovascular variables of the Murray cod have temperature-independent maximum gains that contribute to maximal oxygen transport during exercise. At the expense of a larger factorial aerobic scope at an optimal temperature, as has been reported for species of salmon and trout, it is possible that the Murray cod has evolved a lower, but temperature-independent, factorial aerobic scope as an adaptation to the largely fluctuating and unpredictable thermal climate of southeastern Australia.