Mitochondrial phylogeny within the Yellow Chat (Epthianura crocea) does not support subspecific designation of endangered Alligator Rivers population.

The delineation of subspecies is important in the evaluation and protection of biodiversity. Subspecies delineation is hampered by inconsistently applied criteria and a lack of agreement and shifting standards on how a subspecies should be defined. The Australian endemic Yellow Chat (Epthianura crocea) is split into three subspecies (E. c. crocea, E. c. tunneyi, and E. c. macgregori) based on minor plumage differences and geographical isolation. Both E. c. tunneyi (Endangered) and E. c. macgregori (Critically Endangered) are recognized under Australian legislation as threatened and are the subject of significant conservation effort. We used mitochondrial DNA to evaluate the phylogeny of the Yellow Chat and determine how much genetic variation is present in each of the three subspecies. We found no significant difference in the cytochrome b sequences (833 base pairs) of E. c. crocea and E. c. tunneyi, but approximately 0.70% or 5.83 bp difference between E. c macgregori and both E. c. crocea and E. c. tunneyi. This analysis supports the delineation of E. c. macgregori as a valid subspecies but does not support separation of E. c. crocea from E. c. tunneyi. We also found very low levels of genetic variation within the Yellow Chat, suggesting it may be vulnerable to environmental change. Our results cast doubt upon the geographic isolation of E. c. crocea from E. c. tunneyi, but more advanced genetic sequencing and a robust comparison of plumage are needed to fully resolve taxonomy.

Geographic range size and speciation in honeyeaters.

BACKGROUND: Darwin and others proposed that a species' geographic range size positively influences speciation likelihood, with the relationship potentially dependent on the mode of speciation and other contributing factors, including geographic setting and species traits. Several alternative proposals for the influence of range size on speciation rate have also been made (e.g. negative or a unimodal relationship with speciation). To examine Darwin's proposal, we use a range of phylogenetic comparative methods, focusing on a large Australasian bird clade, the honeyeaters (Aves: Meliphagidae). RESULTS: We consider the influence of range size, shape, and position (latitudinal and longitudinal midpoints, island or continental species), and consider two traits known to influence range size: dispersal ability and body size. Applying several analytical approaches, including phylogenetic Bayesian path analysis, spatiophylogenetic models, and state-dependent speciation and extinction models, we find support for both the positive relationship between range size and speciation rate and the influence of mode of speciation. CONCLUSIONS: Honeyeater speciation rate differs considerably between islands and the continental setting across the clade's distribution, with range size contributing positively in the continental setting, while dispersal ability influences speciation regardless of setting. These outcomes support Darwin's original proposal for a positive relationship between range size and speciation likelihood, while extending the evidence for the contribution of dispersal ability to speciation.

Phylogenetic analyses to uncover the evolutionary relationship of a newly sequenced mitochondrial genome from an Eastern spinebill (Acanthorhynchus tenuirostris).

The Eastern spinebill (Acanthorhynchus tenuirostris), a passerine bird in the family Meliphagidae (honeyeaters), a dominant group of birds in Australia and New Guinea. The aim of this study was to sequence the complete mitochondrial genome of the Eastern spinebill and use its sequence to better define the phylogeny of this species. The complete mitogenome sequence of A. tenuirostris was circular and 16,614 bp in length, and its architecture was conserved in comparison to other mitogenome sequences under the family Meliphagidae. The Eastern spinebill mitogenome had the highest sequence identity with mitogenome sequences of two other honeyeaters, the white eared honeyeater, Nesoptilotis leucotis, (84.9%) and the white-plumed honeyeater, Ptilotula penicillata (85.5%). The maximum-likelihood topology distinctly discriminated the Eastern spinebill sequence against all other species of the Meliphagidae with significant bootstrap supports. We suggest the widespread sampling and complete mitogenome sequencing would be valuable in establishing the most accurate phylogenetic taxonomy of the family Meliphagidae.

Evolution of a multifunctional trait: shared effects of foraging ecology and thermoregulation on beak morphology, with consequences for song evolution.

While morphological traits are often associated with multiple functions, it remains unclear how evolution balances the selective effects of different functions. Birds' beaks function not only in foraging but also in thermoregulating and singing, among other behaviours. Studies of beak evolution abound, however, most focus on a single function. Hence, we quantified relative contributions of different functions over an evolutionary timescale. We measured beak shape using geometric morphometrics and compared this trait with foraging behaviour, climatic variables and song characteristics in a phylogenetic comparative study of an Australasian radiation of songbirds (Meliphagidae). We found that both climate and foraging behaviour were significantly correlated with the beak shape and size. However, foraging ecology had a greater effect on shape, and climate had a nearly equal effect on size. We also found that evolutionary changes in beak morphology had significant consequences for vocal performance: species with elongate-shaped beaks sang at higher frequencies, while species with large beaks sang at a slower pace. The evolution of the avian beak exemplifies how morphological traits can be an evolutionary compromise among functions, and suggests that specialization along any functional axis may increase ecological divergence or reproductive isolation along others.

Frequent nocturnal torpor in a free-ranging Australian honeyeater, the noisy miner.

Torpor in birds is considered to be far less common than in mammals. This is particularly true for passerine birds for which knowledge of torpor expression is scarce, although almost all are small, have high energy expenditure and could profit energetically from using torpor. To assess whether the extent and diversity of avian and especially passerine torpor expression and heterothermy may be currently underestimated because of limited long-term data on free-ranging birds, core body temperature fluctuations were quantified over ~ 4.3 months in a medium-sized honeyeater, the noisy miner (Manorina melanocephala, ~ 75 g), in an open woodland during the cold season in eastern Australia. Miners used shallow nocturnal torpor frequently (63% of days), torpor bouts lasted on average for 6.5 h (maximum 13.5 h) and, unlike during hypothermia, torpor was terminated by endogenous heat production for rewarming. Body temperatures (Tb) ranged from a maximum of 43.5 °C to a minimum of 33.0 °C, often fell by 7 °C at night, and the overall mean Tb was 38.7 ± 0.7 °C. The data show that yet another passerine bird, widely viewed to be homeothermic, expresses torpor in the wild for energy conservation. Considering the size of miners, it seems probable that many other, especially smaller birds, use a similar approach at least in winter to enhance the chance of survival in the face of high energy expenditure and low food availability.

Hybridization following recent secondary contact results in asymmetric genotypic and phenotypic introgression between island species of Myzomela honeyeaters.

Hybridization and introgression can have important evolutionary consequences for speciation, especially during early stages of secondary contact when reproductive barriers may be weak. Few studies, however, have quantified dynamics of hybridization and introgression in systems in which recent natural dispersal across a geographic barrier resulted in secondary contact. We investigated patterns of hybridization and introgression between two Myzomela honeyeaters (M. tristrami and M. cardinalis) that recently achieved secondary contact on Makira in the Solomon Islands. Hybridization in this system was hypothesized to be a byproduct of conspecific mate scarcity during early stages of colonization. Our research, however, provides evidence of ongoing hybridization more than a century after secondary contact. Mitochondrial sequencing revealed strongly asymmetric reproductive isolation that is most likely driven by postzygotic incompatibilities rather than prezygotic behavioral barriers. Nuclear introgression was observed from the native species (M. tristrami) to the colonizing species (M. cardinalis). Nuclear introgression in the reverse direction is almost exclusively limited to birds that are phenotypically M. tristrami but possess M. cardinalis mitochondrial haplotypes, consistent with introgression of plumage-related alleles into the genomic background of M. cardinalis. These results provide unique insight into the dynamics and consequences of hybridization and introgression during early stages of secondary contact.

The compounding effects of high pollen limitation, selfing rates and inbreeding depression leave a New Zealand tree with few viable offspring.

BACKGROUND AND AIMS: Interactions between species are especially sensitive to environmental changes. The interaction between plants and pollinators is of particular interest given the potential current global decline in pollinators. Reduced pollinator services can be compensated for in some plant species by self-pollination. However, if inbreeding depression is high, selfed progeny could die prior to reaching adulthood, leading to cryptic recruitment failure. METHODS: To examine this scenario, pollinator abundance, pollen limitation, selfing rates and inbreeding depression were examined in 12 populations of varying disturbance levels in Sophora microphylla (Fabaceae), an endemic New Zealand tree species. KEY RESULTS: High pollen limitation was found in all populations (average of 58 % reduction in seed production, nine populations), together with high selfing rates (61 % of offspring selfed, six populations) and high inbreeding depression (selfed offspring 86 % less fit, six populations). Pollen limitation was associated with lower visitation rates by the two endemic bird pollinators. CONCLUSIONS: The results suggest that for these populations, over half of the seeds produced are genetically doomed. This reduction in the fitness of progeny due to reduced pollinator service is probably important to population dynamics of other New Zealand species. More broadly, the results suggest that measures of seed production or seedling densities may be a gross overestimate of the effective offspring production. This could lead to cryptic recruitment failure, i.e. a decline in successful reproduction despite high progeny production. Given the global extent of pollinator declines, cryptic recruitment failure may be widespread.

Niche conservatism constrains Australian honeyeater assemblages in stressful environments.

The hypothesis of phylogenetic niche conservatism proposes that most extant members of a clade remain in ancestral environments because expansion into new ecological space imposes a selectional load on a population. A prediction that follows is that local assemblages contain increasingly phylogenetically clustered subsets of species with increasing difference from the ancestral environment of a clade. We test this in Australian Meliphagidae, a continental radiation of birds that originated in wet, subtropical environments, but subsequently spread to drier environments as Australia became more arid during the late Cenozoic. We find local assemblages are increasingly phylogenetically clustered along a gradient of decreasing precipitation. The pattern is less clear along a temperature gradient. We develop a novel phyloclimatespace to visualise the expansion of some lineages into drier habitats. Although few species extend into arid regions, those that do occupy larger ranges and thus local species richness does not decline predictably with precipitation.