David G. Roberts

Marine genetic swamping: hybrids replace an obligately estuarine fish.

Populations of obligately estuarine taxa are potentially small and isolated and may lack genetic variation and display regional differentiation as a result of drift and inbreeding. Hybridization with a wide‐ranging marine congener should introduce genetic variation and reduce the effects of inbreeding depression and genetic drift. However, high levels of hybridization can cause demographic and genetic swamping. In southeastern Australia hybridization occurs between obligately estuarine Black bream (Acanthopagrus butcheri) and migratory marine Yellowfin bream (Acanthopagrus australis). Here, we surveyed genetic variation at eight microsatellite loci and the mitochondrial control region of juvenile fish from five coastal lagoons (including temporal replication in two lagoons) (total n = 970) to determine the frequency and persistence of hybridization, and its likely consequence for the estuarine restricted A. butcheri. Of 688 juvenile fish genotyped 95% were either A. australis (347) or hybrids (309); only 5% (32) were A. butcheri. Most hybrids were later generation hybrids or A. butcheri backcrosses, which are likely multi‐generational residents within lagoons. Far greater proportions of hybrid juveniles were found within two lagoons that are generally closed to the ocean (>90% hybrid fish within generally closed lagoons vs. 12–27% in permanently or intermittently open lagoons). In both lagoons, this was consistent across multiple cohorts of fish [79–97% hybrid fish (n = 282)]. Hybridization and introgression represent a major threat to the persistence of A. butcheri and have yet to be investigated for large numbers of estuarine taxa.

Novel Consequences of Bird Pollination for Plant Mating

Pollinator behaviour has profound effects on plant mating. Pollinators are predicted to minimise energetic costs during foraging bouts by moving between nearby flowers. However, a review of plant mating system studies reveals a mismatch between behavioural predictions and pollen-mediated gene dispersal in bird-pollinated plants. Paternal diversity of these plants is twice that of plants pollinated solely by insects. Comparison with the behaviour of other pollinator groups suggests that birds promote pollen dispersal through a combination of high mobility, limited grooming, and intra- and interspecies aggression. Future opportunities to test these predictions include seed paternity assignment following pollinator exclusion experiments, single pollen grain genotyping, new tracking technologies for small pollinators, and motion-triggered cameras and ethological experimentation for quantifying pollinator behaviour.

Is the post-disturbance composition of a plant population determined by selection for outcrossed seedlings or by the composition of the seedbank?

Seedbanks are expected to buffer populations against disturbances, such as fire, that could alter the genetic composition of smaller, ephemeral adult populations. However, seedling genotypes may be influenced by the spatially heterogeneous nature of both the seedbank and the disturbance (for example, germination may vary with local disturbance) and also by selection acting on germination and post-germination performance. We used microsatellite-DNA surveys of seedlings emerging from the soil-stored seedbanks of Grevillea macleayana after wildfire to compare diversity and spatial structure in seedlings and adults, and through resampling of the seedling data set, to determine whether the resultant adult population reflected the effects of selection or random seedling mortality. The large post-fire seedling cohorts captured the full allelic diversity of the pre-fire adult population. However, we found a mismatch in the genotypic structure of adults and seedlings. Seedlings displayed larger heterozygous deficits than adults; however, over the ensuing 11 years, seedling heterozygosity eventually matched values for the pre-fire adults. Increasing heterozygosity among adults has generally been attributed to heterosis and/or reduction in Wahlund effects via self-thinning. Resampling of early post-fire seedlings to generate samples of equivalent size to survivors at 11 years showed that increases in heterozygosity must be driven by selection favouring outcrossed seed. This finding is important in an evolutionary context but also has implications for the restoration of natural or managed populations where a seedbank is a viable source of recruits.

Small Urban Stands of the Mangrove Avicennia marina are Genetically Diverse but Experience Elevated Inbreeding

Anthropogenic impacts contribute to the fragmentation of urban mangrove forests, and in the Sydney region of Australia, Avicennia marina is commonly found in small stands of <50 adult trees that have altered pollinator services. However, genetic diversity may not vary with stand size because insufficient time has passed since stands were established or pollen and propagule dispersal are sufficient to overwhelm the effects of genetic drift and founder events. We tested the predictions that, despite the potential of mangroves for dispersal of propagules by water and long distance dispersal of pollen by honeybees, fragmentation and localized foraging by honeybees causes small stands of A. marina to display reduced genetic diversity and elevated inbreeding. Using four microsatellite markers, we quantified the genetic and genotypic diversity present within samples of 20 adults taken from three large (>1500 trees), intermediate (300–500 trees) and small (<50 trees) stands within each of two urbanized estuaries and estimated mating system parameters using progeny arrays for sets of five adults within the large and small stands. We detected no significant effect of stand size on levels of single-locus genetic diversity. There were low, although significant, levels of allelic differentiation within (FSE = 0.021, P = 0.003) and among (FET = 0.055, P = 0.005) estuaries but no evidence of isolation by distance. In contrast, our analysis of progeny arrays revealed that, while all stands displayed high levels of biparental inbreeding, an expected consequence of pollination by honeybees, current outcrossing rates (tm) were significantly lower in small (0.55) as compared to large (0.75) stands. The genetic makeup of the adult populations imply that stands are interconnected and suggest little impact of habitat fragmentation, while the progeny arrays suggest that plants within small stands may display reduced fitness.

Microsatellite markers for vulnerable Australian aridzone Acacias

Several Australian arid zone Acacia species are under threat because of decades of fruiting and recruitment failure that may reflect the loss of genetic diversity within small and isolated populations. We developed primers for eight microsatellite loci for Acacia carneorum and Acacia loderi. We detected high levels of clonality in each of two stands of A. carneorum (1 and 2 genets). In contrast, one stand of A. loderi was wholly clonal (1 genet), while in a second there were 30 unique genotypes. These loci allow assessment of the genetic diversity and connectedness of populations, the relative contribution of asexual reproduction to genotypic diversity and population structure, and use of paternity analysis to identify sires of seed within populations known to have set seed in past decades. This type of information may provide a basis for a recovery plan based on ‘genetic rescue’.

Characterizing the biological traits and life history of Acanthopagrus (Sparidae) hybrid complexes: implications for conservation and management.

This study examined the spatio-temporal reproductive patterns, population structure, maturity and growth of Acanthopagrus hybrid complexes, which comprise mainly black bream Acanthopagrus butcheri and the hybrids they form with yellowfin bream Acanthopagrus australis, in two Australian estuaries (Coila and Brou Lakes, NSW). There were no differences between pure A. butcheri and hybrids in terms of their population structure, growth and maturity, suggesting that these two breeds have similar life histories and may therefore be managed as single, naturally cohesive units. Sexual variation in size structure was only observed for the complex in Coila Lake. Although there was significant variation in age structure between estuaries, both complexes exhibited dominance of only a few year classes indicating episodic recruitment and high fishing mortality. Acanthopagrus eggs occurred in higher numbers within upstream creek habitats compared to lake habitats, thereby highlighting the need to protect these spawning habitats. Although maturity in the complexes was not influenced by gender or estuary, differences in growth were detected between the genders and estuaries.

Microsatellite Primers for Vulnerable and Thriving Acacia (Fabaceae) Species from Australia's Arid Zone

Premise of the study: Microsatellite markers were developed for the common arid Australian shrub Acacia ligulata (Fabaceae) and the threatened overstory trees A. melvillei and A. pendula. Methods and Results: DNA sequence data generated by 454 sequencing were used to identify microsatellite nucleotide repeat motifs. Including previously developed primer sets, we report on the development of 10 polymorphic microsatellite loci for each species. Six of these were novel for A. melvillei and A. ligulata, and five were novel for A. pendula, while five more each were transferred from primers developed for related species (A. carneorum and A. loderi). We found three to 17 alleles per locus for each species, with high multilocus genotypic diversity within each of two A. ligulata and A. pendula stands, and one A. melvillei population. A second A. melvillei stand appeared to be monoclonal. Conclusions: These markers will allow assessment of population genetics, mating systems, and connectedness of populations of these and possibly other arid-zone acacias.

Gamete compatibility between marine and estuarine Acanthopagrus spp. (Sparidae) and their hybrids

On Australias south-east coast, hybridization between estuary-restricted black bream Acanthopagrus butcheri Munro and its migratory coastal congener yellowfin bream Acanthopagrus australis (Günther) has led to estuarine populations largely composed of hybrids that are most genetically similar to A. butcheri. The fertilization success achieved when ova of estuary-caught A. butcheri were fertilized with the cryogenically preserved sperm of either ocean-caught A. australis or estuary-caught A. butcheri-like was compared. The experimental crosses, which by chance included both pure parental and hybrid bream, revealed no evidence that gametic incompatibility provides a barrier to fertilization among both pure species and their hybrids.

Characterization and Transferability of Microsatellites for the Kangaroo Paw, Anigozanthos manglesii (Haemodoraceae)

Premise of the study: Microsatellites were developed for the future assessment of population genetic structure, mating system, and dispersal of the perennial kangaroo paw, Anigozanthos manglesii (Haemodoraceae), and related species. Methods and Results: Using a Personal Genome Machine (PGM) semiconductor sequencer, ca. 4.03 million sequence reads were generated. QDD pipeline software was used to identify 190,000 microsatellite-containing regions and priming sites. From these, 90 were chosen and screened using PCR, and 15 polymorphic markers identified. These sites amplified di-, tri-, and pentanucleotide repeats with one to 20 alleles per locus. Primers were also amplified across congeners A. bicolor, A. flavidus, A. gabrielae, A. humilis, A. preissii, A. pulcherrimus, A. rufus, and A. viridis to assess cross-species transferability. Conclusions: These markers provide a resource for population genetic studies in A. manglesii and other species within the genus.

Effectiveness of camera traps for quantifying daytime and nighttime visitation by vertebrate pollinators

Abstract Identification of pollen vectors is a fundamental objective of pollination biology. The foraging and social behavior of these pollinators has profound effects on plant mating, making quantification of their behavior critical for understanding the ecological and evolutionary consequences of different pollinators for the plants they visit. However, accurate quantification of visitation may be problematic, especially for shy animals and/or when the temporal and spatial scale of observation desired is large. Sophisticated heat‐ and movement‐triggered motion‐sensor cameras (“camera trapping”) provide new, underutilized tools to address these challenges. However, to date, there has been no rigorous evaluation of the sampling considerations needed for using camera trapping in pollination research. We measured the effectiveness of camera trapping for identifying vertebrate visitors and quantifying their visitation rates and foraging behavior on Banksia menziesii (Proteaceae). Multiple still cameras (Reconyx HC 500) and a video camera (Little Acorn LTL5210A) were deployed. From 2,753 recorded visits by vertebrates, we identified five species of nectarivorous honeyeater (Meliphagidae) and the honey possum (Tarsipedidae), with significant variation in the species composition of visitors among inflorescences. Species of floral visitor showed significant variation in their time of peak activity, duration of visits, and numbers of flowers probed per visit. Where multiple cameras were deployed on individual inflorescences, effectiveness of individual still cameras varied from 15% to 86% of all recorded visits. Methodological issues and solutions, and the future uses of camera traps in pollination biology, are discussed. Conclusions and wider implications: Motion‐triggered cameras are promising tools for the quantification of vertebrate visitation and some aspects of behavior on flowers. However, researchers need to be mindful of the variation in effectiveness of individual camera traps in detecting animals. Pollinator studies using camera traps are in their infancy, and the full potential of this developing technology is yet to be realized.