Growth and allometry of external morphology in Darwin's finches (Geospiza) on Isla Daphne Major, Galapagos

Seven widely used avian external morphological measurements were examined, mainly in Geospiza fortis and G. scandens on Isla Daphne Major, Galapagos. Geospiza grow more slowly than other "finches", and smaller Geospiza species grow relatively more slowly than larger Geospiza . Weight, wing chord and tarsus grow quickly, while bill characters grow more slowly. This pattern of relative growth (dynamic allometry) is reversed in the static allometry of adults, where bill characters, particularly bill depth in G. fortis , display strong, positive allometry with respect to weight, wing and tarsus. Static allometric patterns help explain differences in the size, shape and relative variability of different characters in adults, as well as the results of multivariate analyses such as principal components or canonical variates. Several different multivariate techniques arrange five Geospiza populations in a consistent two-dimensional morphological space, with a major axis of overall "body-size", and a minor axi of "bill-pointedeness". An alternative analysis of dynamic and static allometry is also provided, based on multivariate techniques.     

Sexual size dimorphism and sex identification using morphological traits of two Aegithalidae species

The black-throated tit, Aegithalos concinnus, and long-tailed tit, A. caudatus, are two widely-distributed species of Aegithalidae. They are thought to be monomorphic and thus difficult to differentiate between sexes in the field. We determined the sex of 296 black-throated tits and 129 long-tailed tits using DNA analysis, evaluated their sexual size dimorphism, and developed discriminant models to identify sex based on morphometries, including bill length, bill depth, bill-head length, maximum tarsus length, tarsus width, wing length, tail length, total body length, and body mass. Both species were sexually dimorphic in size, with males having larger measurements than females, except for bill length in black-throated tits, and both bill length and body mass in long-tailed tits. Moreover, both species showed similar sexual size dimorphism (SSD) among the morphological features, with tail length having the highest SSD value. The multivariate discriminant models for sex identification had an accuracy of 82% for both species, which was slightly higher than the best univariate discriminatory model for each species. Because of the complicated nature of the multivariate model, we recommend univariate models for sex identification using D = 0.491 × tail length - 24.498 (accuracy 80%) for black-throated tits and D = 0.807 × wing length - 45.934 (accuracy 78%) for long-tailed tits. Females in both species showed generally higher morphological variation than did males, resulting in lower accuracies in all discriminate functions regardless of univariate or multivariate approach. This could be the result of a sex-biased selective pressure in which males have higher selective pressures for these morphological features.     

Ancestral polymorphism at the major histocompatibility complex (MHCIIbeta) in the Nesospiza bunting species complex and its sister species (Rowettia goughensis)

ABSTRACT: BACKGROUND: The major histocompatibility complex (MHC) is an important component of the vertebrate immune system and is frequently used to characterise adaptive variation in wild populations due to its co-evolution with pathogens. Passerine birds have an exceptionally diverse MHC with multiple gene copies and large numbers of alleles compared to other avian taxa. The Nesospiza bunting species complex (two species on Nightingale Island; one species with three sub-species on Inaccessible Island) represents a rapid adaptive radiation at a small, isolated archipelago, and is thus an excellent model for the study of adaptation and speciation. In this first study of MHC in Nesospiza buntings, we aim to characterize MHCIIbeta variation, determine the strength of selection acting at this gene region and assess the level of shared polymorphism between the Nesospiza species complex and its putative sister taxon, Rowettia goughensis, from Gough Island. RESULTS: In total, 23 unique alleles were found in 14 Nesospiza and 2 R. goughensis individuals encoding at least four presumably functional loci and two pseudogenes. There was no evidence of ongoing selection on the peptide binding region (PBR). Of the 23 alleles, 15 were found on both the islands inhabited by Nesospiza species, and seven in both Nesospiza and Rowettia; indications of shared, ancestral polymorphism. A gene tree of Nesospiza MHCIIbeta alleles with several other passerine birds shows three highly supported Nesospiza-specific groups. All R. goughensis alleles were shared with Nesospiza, and these alleles were found in all three Nesospiza sequence groups in the gene tree, suggesting that most of the observed variation predates their phylogenetic split. CONCLUSIONS: Lack of evidence of selection on the PBR, together with shared polymorphism across the gene tree, suggests that population variation of MHCIIbeta among Nesospiza and Rowettia is due to ancestral polymorphism rather than local selective forces. Weak or no selection pressure could be attributed to low parasite load at these isolated Atlantic islands. The deep divergence between the highly supported Nesospiza-specific sequence Groups 2 and 3, and the clustering of Group 3 close to the distantly related passerines, provide strong support for preserved ancestral polymorphism, and present evidence of one of the rare cases of extensive ancestral polymorphism in birds.     

Rapid morphological divergence of introduced Red-whiskered Bulbuls Pycnonotus jocosus in contrasting environments

New environmental conditions may impact on behaviour and morphology, and consequently affect population dynamics. Rapid response to new conditions is likely to be a key factor in species introduction success. The Red-whiskered Bulbul Pycnonotus jocosus is an Asian species which, following accidental introduction only 30 years ago, has colonized the two climatically and ecologically contrasting sides of the island of Réunion in the Indian Ocean. We assessed the degree of morphological divergence of mature birds in 11 non-seasonal and three seasonal characters, in windward and leeward sites. Our study showed (1) that sexual dimorphism existed, (2) that when sexual dimorphism is controlled, nine non-seasonal characters differed significantly between windward and leeward sites, (3) that these non-seasonal characters define groups of geographically proximal sites, especially in males, and (4) that classification according to the most indicative character, the bill, also clearly separated birds from windward and leeward sites. These results indicate very rapid morphological divergence, particularly in bill size, in an introduced bird species in fewer than ten generations. We suggest that differences in diet could partly explain this variability.     

The occurrence of two bill morphs of prions Pachyptila vittata on Gough Island

Prions Pachyptila are abundant seabirds in the Southern Ocean that have been used to infer environmental change, but this relies on an understanding of their morphological diversity. Species limits among prions are largely defined by the size and structure of their bills. The broad-billed prion P. vittata, which breeds at temperate islands in the central South Atlantic Ocean and around New Zealand, is the largest species with adult bill widths averaging 21–22 mm. We report local differences in bill sizes on Gough Island, with typical adults breeding in some areas and narrower-billed birds in other areas (average bill width 18–19 mm, although at one site there was a second mode at bill widths of 16–17 mm). The narrow-billed birds have slightly shorter bills, heads and wings (averaging 1–2 % smaller than typical adult broad-billed prions), but the difference in bill width is much more marked (15 %). The small-billed birds differ from typical broad-billed prions in having blue colouration in the upper mandible and are similar in size to MacGillivray’s prion P. [salvini/vittata] macgillivrayi from Amsterdam and St Paul islands in the temperate Indian Ocean. The occurrence of two prion morphs on Gough Island raises intriguing questions about their ecology and systematics. Small-billed birds breed 3 months later than large-billed birds, suggesting that they are a separate species, not an example of bill polymorphism.     

青藏高原褐背拟地鸦表型特征的性别差异与地理变异

将数值分类用于鸟类分类学研究时,对于雌雄的形态特征差异没有被重视,尤其是对于雌雄同形的鸟类。本文以雌雄同形的褐背拟地鸦Pseudopodoces humilis为材料,运用SPSSl0．0FORwINDOwS统计分析软件对108号褐背拟地鸦标本(51♀♀,57♂♂)的数量性状(体长、跗跖长、翅长、尾长、嘴宽、嘴高、上喙长、下喙长、嘴裂、第3趾爪长、第1趾爪长)的原始数据进行分析,结果表明雌、雄性状在翅长(n＝51,P＝0．012)和嘴高(n＝57,P＝0．043)上有明显差异,但在体长、跗跖长、尾长、嘴宽、上喙长、下喙长、嘴裂、第3趾爪长、第1趾爪长等数值特征上却没有明显的差异。所以在以后对于褐背拟地鸦的地理种群变异和亚种分化的研究中,翅长和嘴高两特征应该根据雌雄分别讨论。通过对不同性状量度和纬度的相关回归分析,发现在测量标本所涉及的采集地范围内,即主要在青藏高原东南部地区,褐背拟地鸦体长和雄乌的翅长在地理分布上随纬度的增加而变小,而其它性状特征没有明显的地理分布纬度上的变化。     

基于形态特征判定五种鹬类性别的可靠性

快速准确地鉴定两性同型鸟类个体性别在鸟类生态学研究中具有重要意义。本文选择2008年春季迁徙期在崇明东滩停歇的大滨鹬(Calidris tenuirostris)、红腹滨鹬(C.canutus)、红颈滨鹬(C.ruficollis)、尖尾滨鹬(C.acuminata)及翘嘴鹬(Xenus cinereus)5种两性同型的鹬类,用分子生物学方法进行性别鉴定,并基于个体的形态特征(体重、翅长、喙长、头喙长及跗跖长)采用判别分析方法对性别进行判定。结果表明,尖尾滨鹬雄性各形态特征均显著大于雌性,其他4种鹬类则相反。5种鹬类形态特征的性别差异指数在0.5%~25.3%之间,重叠度在29.4%~98.6%之间。5种鹬类判别分析判定性别的准确率在(0.69±0.06)~(0.96±0.01)之间,其中,尖尾滨鹬判别准确率(0.96)最高,翘嘴鹬判别准确率(0.69)最低。形态特征在两性间的差异程度影响性别的判别准确率。另外,两性性比对性别判别的准确率也有影响:性比偏雄性鸟类的雄性判别准确率高于雌性,而性比偏雌性鸟类的雌性判别准确率高于雄性。采用判别分析估测的性比与分子生物学鉴定结果相似,表明判别分析在判定种群的性比方面具有较高的可靠性。     

Rapid evolution of great kiskadees on Bermuda: an assessment of the ability of the island rule to predict the direction of contemporary evolution in exotic vertebrates

Aim To determine whether an exotic bird species, the great kiskadee (Pitangus sulphuratus), has diverged in morphology from its native source population, and, if so, has done so in a manner predicted by the island rule. The island rule predicts that insular vertebrates will tend towards dwarfism or gigantism when isolated on islands, depending on their body size. For birds, the island rule predicts that species with body sizes below 70–120 g should increase in size. The great kiskadee has a mean mass of c. 60 g in its native range, therefore we predicted that it would increase in size within the exotic, and more insular, Bermudan range. Location The islands of Bermuda (exotic population) and Trinidad (native source population). Methods We took eight morphological measurements on 84 individuals captured in the exotic (Bermudan) population and 62 individuals captured in the native source (Trinidadian) population. We compared morphological metrics between populations using univariate and principal components analyses. We assessed whether the effects of genetic drift could explain observed differences in morphology. We calculated divergence rates in haldanes and darwins for comparison with published examples of contemporary evolution. Finally, we used mark–recapture analysis to determine the effects of the measured morphological characters on survivorship within the exotic Bermudan population. Results Individuals in the exotic Bermudan population have larger morphological dimensions than individuals in the native source population on Trinidad. The degree of divergence in body mass (g) and bill width (mm) is probably not due to genetic drift. This rate of divergence is nearly equal to that observed amongst well‐documented examples of contemporary bird evolution, and is within the mid‐range of rates reported across taxa. There is no clear effect of body size on survivorship as only one character (bill width) was found to have an influence on individual survivorship. Main conclusions Exotic species provide useful systems for examining evolutionary predictions over contemporary time‐scales. We found that divergence between the exotic and native populations of this bird species occurred over c. 17 generations, and was in the direction predicted by the island rule, a principle based on the study of native species.     

Evolutionary ecology and radiation of Hawaiian passerine birds

The Hawaiian islands contain the most spectacular variety of landbirds ever discovered on remote oceanic islands. The Hawaiian honeycreepers, having evolved from a presumably single founding species of cardueline finch, comprise most of this avifauna. Birds from at least three other families of passerines and five families of non-passerines also radiated in Hawaii. Recent discoveries of a fossil avifauna indicate that most radiations were more extensive than previously thought. Classical analysis of the radiation of Hawaiian birds, especially the honeycreepers, focused on characters related to acquisition of food. Recent studies of bill size and shape in relation to food resources, and of foraging mode in relation to interspecific competitors, provide models of how divergence in diet and/or bill morphology might have evolved. Studies of geographic variation among subspecies on different islands and among populations within islands have revealed extensive divergence in characters such as sexual chromatism, nest sites and nest morphology.     

Species delimitation and the origin of populations in island representatives of Phylica (Rhamnaceae)

Abstract Relationships between the closely related island species of Phylica (Rhamnaceae) and a mainland species, P. paniculata , were elucidated using amplified fragment length polymorphisms (AFLPs). Parsimony, neighbor joining, and principal coordinate (PCO) analyses indicated that each of the species studied is distinct. AFLPs were also useful in elucidating the genetic relationships and possible infraspecific origins of different island populations in the Atlantic and Indian Oceans. Phylica nitida on Réunion is likely to have been derived from P. nitida on Mauritius. Although the sampling on New Amsterdam is not extensive, the data are also consistent with the hypothesis that P. arborea on New Amsterdam was derived from a single colonization of P. arborea from Gough Island. Similarly, the Gough Island population appears to have been derived from a single colonization event, but it is so distinct from those on Tristan da Cunha, that there may have been two separate dispersals to Gough and Tristan/Nightingale from different lines of the mainland progenitor. There is also evidence of a recolonization from Gough to Tristan da Cunha. Thus, Phylica arborea is capable of repeated long distance dispersal, up to 8000 km, even though the fruits and seeds are not of a type normally associated with this phenomenon.     

Geographic variation in Austrolebias luteoflamulatus Vaz‐Ferreira, Sierra & Scaglia (Cyprinodontiformes, Rivulidae)

The morphological variation in the annual killifish Austrolebias luteoflamulatus was studied using meristic and pigmentation characters analysed with univariate and multivariate analysis, and morphometric characters analysed with a geometric morphometry approach (thin plate spline). The results showed that morphological variation in this species was associated with a geographical pattern. In the case of meristic and pigmentation characters, the strongest distinction occured in males, while females were more similar among different drainages. Males from Rocha (eastern Uruguay) exhibited the greatest differences from the others. The number of dorsal fin rays and bars on the flanks were the characters that contributed most to this segregation. When morphometrics were considered, the three populations analysed could be distinguished well from each other in both sexes. Some of the characters that contributed to this pattern were dorsal fin origin, position of eyes and length of snout. Since pigmentation characteristics and some characters of the dorsal fin in males were involved in the differences observed, sexual selection could have played an important role in the differentiation of populations of this species. Since Austrolebias luteoflamulatus has a restricted geographical distribution, conservation of this species should include consideration of these populations individually since they might represent different evolutionary units.     

Asymmetrical expression of transsexual phenotypes in hummingbirds

I present evidence for asymmetry in the expression of transsexual traits in adult hummingbirds. Among females, individuals with male-like plumage are common and define a continuous range of variation. Among males, individuals with female-like plumage are rare and define discontinuous plumage morphs. Quantitative characters also distinguish transsexuals from other members of their sex, but the characters involved differ for male-like females (bill length) and female-like males (bill, wing and tail length). Gonadal development is correlated with transsexuality only in males; female-like males have significantly smaller testes than male-like males. Both sexes demonstrate a significant negative association between plumage brightness and bill length. This association suggests an ecological basis for transsexuality because differences in plumage and bill morphology are associated with differences in foraging behaviour within and between hummingbird species. Morphological differences between transsexuals and non-transsexuals imply that plumage sexual dimorphism is more likely to evolve through changes in the frequency of female, rather than male, transsexual variants.     

Rates of species introduction to a remote oceanic island

The introduction of species to areas beyond the limits of their natural distributions has a major homogenizing influence, making previously distinct biotas more similar. The scale of introductions has frequently been commented on, but their rate and spatial pervasiveness have been less well quantified. Here, we report the findings of a detailed study of pterygote insect introductions to Gough Island, one of the most remote and supposedly pristine temperate oceanic islands, and estimate the rate at which introduced species have successfully established. Out of 99 species recorded from Gough Island, 71 are established introductions, the highest proportion documented for any Southern Ocean island. Estimating a total of approximately 233 landings on Gough Island since first human landfall, this equates to one successful establishment for every three to four landings. Generalizations drawn from other areas suggest that this may be only one-tenth of the number of pterygote species that have arrived at the island, implying that most landings may lead to the arrival of at least one alien. These rates of introduction of new species are estimated to be two to three orders of magnitude greater than background levels for Gough Island, an increase comparable to that estimated for global species extinctions (many of which occur on islands) as a consequence of human activities.     

NATURAL SELECTION ON BILL CHARACTERS IN THE TWO BILL MORPHS OF THE AFRICAN FINCH PYRENESTES OSTRINUS

Evidence for natural selection on seven bill and body characters is examined in the two bill morphs of the African estrildid finch Pyrenestes ostrinus. Two regression methods are used in examining natural selection in association with survivorship: a parametric (Lande and Arnold, 1983) and a non-parametric (Schluter, 1988) method. Selection was estimated in adult males, females and juveniles over a four-year period in a population in south-central Cameroon. Selection was common among groups but patterns differed and depended on the method used in detecting selection. The non-parametric method revealed evidence for disruptive selection occurring on bill width and is explained within the context of known feeding efficiencies and the hardness of important seeds in finch diets. Directional selection was common on bill characters in all groups, but infrequent on other characters. There was no evidence of selection on generalized size or shape characters. Selection on bill characters was common across groups despite low annual variation in rainfall. This contrasts with studies of Galápagos finches in which selection is frequently associated with dramatic changes in food supply caused by high variance in annual rainfall. Patterns of selection on bill traits in P. ostrinus also differ from those in song sparrows and Galápagos finches by exhibiting evidence for natural selection on all bill dimensions.     

Morphological differentiation in Carduelis finches: Adaptive vs. constraint models

In this study we show that morphological diversification in the avian genus Carduelis (Carduelinae) has to a large extent been conservative. Using multivariate methods, we found only minor deviations from the common (ancestral) body-plan. In particular, variation in bill morphology was found to be more conservative than variation in other parts of the body. We argue that constraint models of population differentiation can successfully account for the variation in bill morphology in this genus, but are less successful in accounting for variation in other traits. This can be interpreted as a result of long-term overall stabilizing selection for a certain bill morphology which is related to the way the birds open seeds. A trait combination that is adaptive on the evolutionary time scale may thus act as a constraint on changes in bill morphology on the microevolutionary scale. We conclude that the most parsimonious explanation for low divergence in bill morphology in this genus is that all species have retained the ancestral bill morphology. This may mean that each species chooses its environment rather than being moulded by it. This argument seems to apply to bill morphology, but other traits studied in this genus appear to have evolved in a less constrained fashion. A new index of morphometric integration is introduced to describe covariance structures.     

Geographic variation in the Laysan Finch (Telespyza cantans)

Summary Significant differences in bill shape exist between the endemic Laysan population and introduced populations of the Laysan Finch (Drepanidinae:Telespyza cantans) at Pearl and Hermes Reef. Furthermore, there are significant differences in bill shape between two of four finch populations on the islands of Pearl and Hermes Reef. The variation in finch bill shape is paralleled by geographic variation in the large, hard mericarps ofTribulus cistoides, an important food item at Pearl and Hermes Reef. There are three possible explanations for the observed variation. Environmental influence may be a non-evolutionary cause of the variation, or genetic drift and natural selection may have caused the differences in morphology. Preliminary results suggest that both genetic drift and natural selection have been acting on the populations. Continuing studies, including investigation of genetic variation and cross-fostering experiments to determine heritability of morphological traits and effects of environment on morphological traits, are planned to test the various hypotheses.     

The impacts of introduced House Mice on the breeding success of nesting seabirds on Gough Island

Invasive species are the main threat to island biodiversity; seabirds are particularly vulnerable and are one of the most threatened groups of birds. Gough Island, a UNESCO World Heritage Site in the South Atlantic Ocean, is an Important Bird and Biodiversity Area, and one of the most important seabird colonies globally. Invasive House Mice Mus musculus depredate eggs and chicks of most seabird species on the island, but the extent of their impact has not been quantified. We used field data and bootstrapped normal distributions to estimate breeding success and the number of surviving chicks for 10 seabird species on Gough Island, and compared estimates with those of analogous species from predator‐free islands. We examined the effects of season and nest‐site location on the breeding success of populations on Gough Island, predicting that the breeding success of Gough birds would be lower than that of analogues, particularly among small burrow‐nesting species. We also predicted that winter‐breeding species would exhibit lower breeding success than summer‐breeding species, because mice have fewer alternative food sources in winter; and below‐ground nesters would have lower breeding success than surface nesters, as below‐ground species are smaller so their chicks are easier prey for mice. We did indeed find that seabirds on Gough Island had low breeding success compared with analogues, losing an estimated 1 739 000 (1 467 000–2 116 000) eggs/chicks annually. Seven of the 10 focal species on Gough Island had particularly high chick mortality and may have been subject to intense mouse predation. Below‐ground and winter breeders had lower breeding success than surface‐ and summer‐breeders. MacGillivray's Prion Pachyptila macgillivrayi, Atlantic Petrel Pterodroma incerta and Tristan Albatross Diomedea dabbenena are endemic or near‐endemic to Gough Island and are likely to be driven to extinction if invasive mice are not removed.     

Inferring phylogenetic patterns of land snails of the genus Albinaria on the island of Dia (Crete,Greece)

Albinaria (Gastropoda, Clausiliidae) is a pulmonate genus distributed around the north-eastern coasts of the Mediterranean. It is the most 'speciose' genus within the family of Clausiliidae, exhibiting a high degree of morphological and genetic differentiation, and serving as a model for several ecological, systematics and evolutionary studies. Nevertheless, many aspects remain uncertain mainly due to the large number of taxa whose classification has not yet been evaluated with solid synapomorphic characters. Thirty-one morphological species are currently recognized on the island of Crete and its satellite islets. Four of them (A. retusa, A. torticollis, A. jaeckeli, and A. teres) are distributed on the island of Dia (north of Crete); the first three are island endemics. Here, we combined mitochondrial and nuclear DNA information and Bayesian and Maximum Likelihood approaches to evaluate the phylogenetic relationships, and assess the genetic distinctiveness and cohesiveness of all described species of Dia Island. The produced phylogeny was not congruent with the morphological species, demonstrating a more complex pattern of speciation and diversification. Although each island endemic constitutes a monophyletic lineage, the number of island endemic species could be greater than the three currently recognized species so far (A. retusa, A. torticollis, and A. jaeckeli), since a newly discovered lineage (north-western part of the island), that morphologically differs from the populations of A. torticollis in the eastern part, and genetically is more closely related to A. jaeckeli, could be elevated to the species level. Considering the fourth species found on the island of Dia, A. teres is genetically highly variable, showing low geographic structuring due to either long-distance gene flow or retained ancestral polymorphisms, or a combination of both. Further work (analysis of more specimens and DNA data) both from Dia and Crete is indispensable in order to shed light on aspects of the evolutionary history of the genus in Dia.