Climate niche differentiation between two passerines despite ongoing gene flow.

Niche evolution underpins the generation and maintenance of biological diversity, but niche conservatism, in which niches remain little changed over time in closely related taxa, and the role of ecology in niche evolution are continually debated. To test whether climate niches are conserved in two closely related passerines in East Asia - the vinous-throated (Paradoxornis webbianus) and ashy-throated (P. alphonsianus) parrotbills - we established their potential allopatric and sympatric regions using ecological niche models and compared differences in their climate niches using niche overlap indices in background tests and multivariate statistical analyses. We also used polymorphism data on 44 nuclear genes to infer their divergence demography. We found that these two parrotbills occupy different climate niches, in both their allopatric and potential sympatric regions. Because the potential sympatric region is the area predicted to be suitable for both parrotbills based on the ecological niche models, it can serve as a natural common garden. Therefore, their observed niche differences in this potential sympatry were not simply rendered by phenotypic plasticity and probably had a genetic basis. Our genetic analyses revealed that the two parrotbills are not evolutionarily independent for the most recent part of their divergence history. The two parrotbills diverged c. 856,000 years ago and have had substantial gene flow since a presumed secondary contact c. 290,000 years ago. This study provides an empirical case demonstrating that climate niches may not be homogenized in nascent species in spite of substantial, ongoing gene flow, which in turn suggests a role for ecology in promoting and maintaining diversification among incipient species.

Responses of cuckoo hosts to alarm signals of different nest intruders in non-nesting areas.

The "call for help" hypothesis proposes that alarm calls produced by a bird can transmit warning information to both conspecific and interspecific neighbors. Neighbors who are attracted by social transmission might benefit from knowing about the presence of danger or by gaining information about the presence of predators or brood parasites nearby. Brood parasite hosts can distinguish threats from different intruders and exhibit varied responses correspondingly. However, most previous studies have conducted sound playback at host nest sites and focused on conspecific individuals attracted by the alarm calls. In this study, we used random location playback to investigate the responses of different host species to alarm signals of oriental reed warblers (Acrocephalus orientalis) toward different intruders (brood parasite, predator, and harmless control) in order to reveal how hosts evaluate different threats from different intruders using vocal information in non-nesting areas during the breeding season. We found that the alarm calls given in response to different intruders incurred similar numbers of approaching species for both conspecific and interspecific birds. However, the number of attracted individuals differed significantly among the various species, with conspecifics and vinous-throated parrotbills (Paradoxornis webbianus) dominating, both of which are major hosts of common cuckoos (Cuculus canorus). Nevertheless, interspecific birds did not present any aggressive behavior according to the alarm calls, which implied that visual information may be needed for further confirmation of threats. In addition, determining whether alarm call structure promoted an evolutionary convergence phenomenon still needs further verification.

Egg recognition abilities of tit species in the Paridae family: do Indomalayan tits exhibit higher recognition than Palearctic tits?

Recent studies have shown that the closely related cinereous tit ( Parus cinereus) and green-backed tit ( P. monticolus) in China display strong egg recognition ability in contrast to tit species in Europe, which lack such ability. However, egg recognition in other populations of cinereous and green-backed tits and additional Paridae species still requires further research. Here, we compared the egg recognition abilities of cinereous tits across China, green-backed tits ( P. m. insperatus) in Taiwan, China, and five other species from the Paridae family, including the marsh tit ( Poecile palustris), varied tit ( Sittiparus varius), willow tit ( Poecile montanus), coal tit ( Periparus ater), and ground tit ( Pseudopodoces humilis). Results showed that the Hebei (58.8% egg rejection, n=17) and Liaoning populations (53.3%, n=15) of cinereous tits, and the Guizhou (100%, n=12) and Taiwan populations (75%, n=12) of green-backed tits all exhibited high egg recognition ability. The egg recognition ability of these tits was significantly greater than that of the other five species in the Paridae family. The varied tit (5.4%, n=37), marsh tit (8.3%, n=12), willow tit (Hebei: 25%, n=20; Beijing: 9.5%, n=21), coal tit (16.7%, n=18), and ground tit (0, n=5) species all showed low egg recognition abilities, with no significant differences found among them. Egg recognition was not associated with a single phylogenetic group but occurred in several groups of tits. In particular, those species widely distributed in the Indomalayan realm, thus overlapping with small cuckoo species, displayed strong egg recognition ability, whereas tit species in the Palearctic realm exhibited low or no egg recognition ability.

Nest sanitation facilitates egg recognition in the common tailorbird, a plaintive cuckoo host.

Nest sanitation is a ubiquitous behavior in birds and functions to remove foreign objects that accidentally have fallen into their nests. In avian brood parasitism, the host's ability to recognize and reject parasitic eggs is a specific anti-parasitic behavior. Previous studies have shown that egg recognition may have evolved from nest sanitation behavior; however, few studies have offered evidence in support of this hypothesis. In the current study, we added one real white egg and one model egg to the nests of common tailorbirds (Orthotomus sutorius), the main host of plaintive cuckoos (Cacomantis merulinus), to explore the relationship between egg recognition ability in hosts and nest sanitation behavior. Results showed that common tailorbirds rejected both non-mimetic blue model eggs and mimetic white model eggs at a similar rate of 100%, but only rejected 16.1% of mimetic real white eggs. The egg rejection behavior of common tailorbirds towards both real and model eggs was consistent. However, when both blue model eggs and real white eggs were simultaneously added to their nests, the probability of rejecting the mimetic real white egg increased to 50%. The addition of blue model eggs not only increased the occurrence of nest sanitation behavior but also increased the ability to recognize and reject parasitic eggs. This suggests that nest sanitation may facilitate egg rejection in common tailorbird hosts.

High egg rejection rate in a Chinese population of grey-backed thrush (Turdus hortulorum).

everal previous studies have indicated that nest sanitation behavior is a general adaptation in altricial birds, with egg recognition capacity evolving as a specific response to interspecific brood parasitism (IBP). However, a recent study suggested an alternative hypothesis, concluding that conspecific brood parasitism (CBP) selects for egg rejection in thrushes, with IBP as a by-product. In the present study, we used a spectrophotometer to quantify egg coloration and egg mimicry and performed artificial parasitism experiments in the grey-backed thrush (Turdus hortulorum). We showed that individuals of this species rejected 100% of 12 foreign eggs, without IBP or CBP detected. In a review of previous studies, we also discuss possible explanations for the high egg rejection rate in the grey-backed thrush and suggest areas for future study.

Geographic variation in parasitism rates of two sympatric cuckoo hosts in China.

Rates of brood parasitism vary extensively among host species and populations of a single host species. In this study, we documented and compared parasitism rates of two sympatric hosts, the Oriental Reed Warbler (Acrocephalus orientalis) and the Reed Parrotbill (Paradoxornis heudei), in three populations in China. We found that the Common Cuckoo (Cuculus canorus) is the only parasite using both the Oriental Reed Warbler and Reed Parrotbill as hosts, with a parasitism rate of 22.4%-34.3% and 0%-4.6%, respectively. The multiple parasitism rates were positively correlated with local parasitism rates across three geographic populations of Oriental Reed Warbler, which implies that higher pressure of parasitism lead to higher multiple parasitism rate. Furthermore, only one phenotype of cuckoo eggs was found in the nests of these two host species. Our results lead to two conclusions: (1) The Oriental Reed Warbler should be considered the major host of Common Cuckoo in our study sites; and (2) obligate parasitism on Oriental Reed Warbler by Common Cuckoo is specialized but flexible to some extent, i.e., using Reed Parrotbill as a secondary host. Further studies focusing on egg recognition and rejection behaviour of these two host species should be conducted to test our predictions.

[Using spectra and visual modeling to study animal coloration].

Animal coloration has many adaptive functions and plays an important role in signal communication both among intra- and interspecies. For example, it has been widely used in mate choice, intrasexual competition, and as aposematic or cryptic coloration in predator avoidance. Many colors and pigments also function in microbial resistance, structural support, photoprotection, and thermoregulation. Differing from human vision, based on RGB system, many other animals have tetrachromatic vision system, which includes the ultraviolet (UV) range that is undetectable by human eyes. Previous studies showed that ultraviolet is important in some species' social signaling and communication. Moreover, cone inner segments of most classes of vertebrate contain an oil droplet, which acts as a cut-off filter absorbing wavelengths below a critical value, and transmitting longer wavelengths. Animal and human vision is significantly different in that the classification of color by human standards may be a misleading for measuring animal coloration. Here, we illuminate how to use fiber spectrophotometer to quantify animal coloration, and analyze it by spectra analysis and visual modeling. As an example, we obtained plumage reflectance spectra from male and female scarlet minivets (Pericrocotus flammeus). This bird species is sexually dimorphic that the males have plumage color in black and red, while the females have grey and yellow accordingly. These plumage colors are typically generated from melanin and carotenoid pigments, which have an effect on antioxidant activity. Analysis of spectra segments provides hue, chroma, brightness and relative brightness of each wave range. Visual modeling maps color patches on tetrahedral color space and Robinson projection, meanwhile, calculates color span and color space volume which describe the color contrast and color diversity, respectively. In visual modeling, ambient light irradiance and spectral sensitivity of animal retinas are included, which provides an objective evaluation of coloration of animal vision.

[Spectra analysis reveals the sexual dichromatism of red-eared slider turtle(Trachemys scripta)].

In this study,spectra analysis was conducted to investigate the sexual dichromatism and relationship between body color and quality of the red-eared slider turtle (Trachemys scripta). Visual modeling revealed that the differences of the hues of body colors' ultraviolet (UV) components between male and female were significant. Moreover, the visible(VIS)components of the hues of forelimbs were correlated with body qualities of male but not of female. Our results indicated that UV might act as a signal for sexual cognition in red-eared slider turtles, and female might evaluate male by the VIS components of the hues of forelimbs. These findings provided preliminary results and perspectives to the sexual dichromatism and sexual selection behaviors of red-eared slider turtles.

Visual modeling reveals cryptic aspect in egg mimicry of Himalayan Cuckoo (Cuculus saturatus) on its host Blyth's Leaf Warbler (Phylloscopus reguloides).

Brood parasitism and egg mimicry of Himalayan Cuckoo (Cuculus saturatus) on its host Blyth's Leaf Warbler (Phylloscopus reguloides) were studied in south-western China from April to July 2009. The cuckoo laid a white egg with fine brown markings on the blunt end. The eggs were conspicuously bigger than the host's own, with 2.06 g in mass and 1.91 cm(3) in volume. Visual modeling showed that the cuckoo eggs, which from the human eye appeared to mimic the host eggs to a great extent, were completely different from the host eggs in both hue and chroma. The characters of the Himalayan Cuckoo nestling, reported for the first time, included two triangular and black patches on its gape, which appeared from four days old and became darker with age and growth. While this character also exists in nestlings of Oriental Cuckoo (C. optatus), it has not been found for other Cuculus species. Our results reveal cryptic aspects in the cuckoo-host egg color matching, which are not visible to the naked human eye, and indicate that high mimetic cuckoo eggs rejected by hosts, as determined by human observers in previous studies, might not be mimetic as birds see them.

[Brood parasitism and egg mimicry on Brownish-flanked Bush Warbler (Cettia fortipes) by Lesser Cuckoo (Cuculus poliocephalus)].

Nest fate of Brownish-flanked Bush Warbler (Cettia fortipes) was conducted in breeding seasons from 1999 to 2009 in Kuankuoshui Natural Reserve, Guizhou province. Predation rate, parasitism rate, hatching success, nesting success and reproductive success were surveyed and egg color was quantified using spectrophotometer. Principal component analysis, reflectance spectrum and Robinson Project were used to analyze the egg color of bush warbler and egg mimicry of Lesser Cuckoo (Cuculus poliocephalus) in parasitized nests. Our results indicated that the Brownish-flanked Bush Warbler suffered from high predation rate and relatively high parasitism rate of 49.26% and 9.18%, respectively. Reflectance analysis showed that the hue and chroma of Lesser Cuckoo eggs were highly mimetic but the egg brightness and ultraviolet reflectance were different from the bush warbler.