Life in a Double-Hotspot: The Transformation of Hawaiian Passerine Bird Diversity following Invasion and Extinction

Although recent research has shown that non-indigenous species often increase local-scale species richness, few have documented how such increases translate into compositional changes across biological scales. In particular, transformations of biodiversity patterns may be acute within regions that are simultaneously extinction and invasion hotspots (i.e. double-hotspots), such as the Hawaiian Islands. Nevertheless, modification of diversity relationships in such places are rarely quantified. Here, I utilize passerine non-indigenous species introductions and native species extinctions on Hawaii to quantitatively explore the changing relationship between within- (alpha), between- (beta), and across-island (gamma) diversity. My results indicate that, even after incorporating the enrichment effects of non-indigenous species invasions, across-island passerine diversity has dropped substantially. Nevertheless, within-island diversity has remained largely unchanged, or in some cases increased. Perhaps the more profound changes in diversity have come from the loss of between-island diversity. Because nearly all native Hawaiian passerines are extinct or near extinction, the current diversity relationships are inordinately influenced by patterns in the transportation and establishment of non-indigenous birds. These human-induced ‘dispersal’ patterns are markedly different from natural ones. In addition, these dispersal patterns may be unique to vagile species such as birds, thus indicating that transformations of diversity within other groups (e.g. plants or freshwater fishes) currently inhabiting Hawaii may differ. These results suggest the need to explore how alteration of diversity relationships translate into the loss of ecosystem services, or other valued components of biodiversity.     

灰椋鸟身体大小和内脏器官形态的两性差异

鸟类性二态现象广泛存在,比如身体大小、羽色等,性二态很可能是自然选择和性选择共同作用的结果.为了探索和更好地了解雀形目鸟类身体大小性二态的进化,在2019年繁殖季节早期研究了灰椋鸟(Sturnus cineraceus)野外种群身体大小和内脏器官形态的两性差异.结果表明,除嘴宽外,其他身体特征参数均雄性显著大于雌性,表...     

Increased Endoparasite Infection in Late-Arriving Individuals of a Trans-Saharan Passerine Migrant Bird

Earlier migration in males than in females is the commonest pattern in migrating passerines and is positively related to size dimorphism and dichromatism. The early arrival of males is a costly trait that may confer reproductive advantages in terms of better territories and/or mates. Given the physiological cost of migration, early migrants are those in best condition and accordingly the prevalence, load, and/or diversity of parasites is expected to increase in both sexes for late migrants. To test this hypothesis, we sampled 187 trans-Saharan migrant garden warblers Sylvia borin and 64 resident serins Serinus serinus (as a control for potential circannual patterns in parasite load) during spring migration in Spain. We assessed the prevalence of blood parasites (Haemoproteus, Plasmodium, and Leucocytozoon) and the prevalence and load of intestinal parasites (mainly coccidians and spirurids). The relationship between parasite (prevalence, load, and richness) and the timing of passage through a stopover area was tested using generalized linear models. Protandry occurs in the monomorphic garden warbler and males migrated on average 5.5 days before females. Intestinal parasite richness increased with the date of migration. The timing of migration was unrelated to the presence or load of the other parasite groups analyzed. Our results support the idea that the timing of migration is a condition-dependent trait and suggests that multiple intestinal parasite infestations could delay migration in birds. Even in monomorphic species parasites may play a role in sexual selection by delaying the arrival of the most infected individuals at breeding grounds, thereby further increasing the benefits of mating with early-arriving individuals.     

The PHA Test as an Indicator of Phagocytic Activity in a Passerine Bird

Several techniques in ecological immunology have been used to assess bird immunocompetence thus providing useful information to understand the contribution of the immunological system in life-history decisions. The phytohaemagglutinin (PHA)-skin test has been the most widely employed technique being interpreted as the sole result of T lymphocytes proliferation and hence used to evaluate acquired immunological capacity. However, the presence of high numbers of phagocytic cells in the swelling point has cast some doubt about such an assumption. To address this issue, we collected blood from 14 days-old nestlings of spotless starling (Sturnus unicolor), administered subcutaneous PHA immediately after and then measured the swelling response 24 hours later. Differential counts of white blood cells suggested that an intense development of acquired immunological defences was taking place. The phagocytic activity of both heterophiles and monocytes was also very intense as it was the swelling response. Moreover, our results show, for the first time in birds, a positive relationship between the phagocytic activity of both kinds of cells and the swelling response. This broadens the significance of the PHA test from reflecting T lymphocytes proliferation -as previously proposed but still undetermined in vivo- to evaluate phagocytosis as well. In other words, our data suggest that the PHA swelling response may not be considered as the only consequence of processes of specific and induced immunity –T lymphocytes proliferation- but also of constitutive and nonspecific immunity –heterophiles and monocytes phagocytosis. We propose the extensive use of PHA-skin test as an optimal technique to assess immunocompetence.     

Effects of Temperature on Circadian Clock and Chronotype: An Experimental Study on a Passerine Bird

Daily schedules of many organisms, including birds, are thought to affect fitness. Timing in birds is based on circadian clocks that have a heritable period length, but fitness consequences for individuals in natural environments depend on the scheduling of entrained clocks. This chronotype, i.e., timing of an individual relative to a zeitgeber, results from interactions between the endogenous circadian clock and environmental factors, including light conditions and ambient temperature. To understand contributions of these factors to timing, we studied daily activity patterns of a captive songbird, the great tit (Parus major), under different temperature and light conditions. Birds were kept in a light (L)-dark (D) cycle (12.5?L:11.5 D) at either 8°C or 18°C with ad libitum access to food and water. We assessed chronotype and subsequently tested birds at the same temperature under constant dim light (LL_dim) to determine period length of their circadian clock. Thermal conditions were then reversed so that period length was measured under both temperatures. We found that under constant dim light conditions individuals lengthened their free-running period at higher temperatures by 5.7?±?2.1?min (p?=?.002). Under LD, birds kept at 18°C started activity later and terminated it much earlier in the day than those kept under 8°C. Overall, chronotype was slightly earlier under higher temperature, and duration of activity was shorter. Furthermore, individuals timed their activities consistently on different days under LD and over the two test series under LL_dim (repeatability from .38 to .60). Surprisingly, period length and chronotype did not show the correlation that had been previously found in other avian species. Our study shows that body clocks of birds are precise and repeatable, but are, nonetheless, affected by ambient temperature. (Author correspondence: marina.lehmann@uni-konstanz.de)     

Maternal Condition but Not Corticosterone Is Linked to Offspring Sex Ratio in a Passerine Bird

There is evidence of offspring sex ratio adjustment in a range of species, but the potential mechanisms remain largely unknown. Elevated maternal corticosterone (CORT) is associated with factors that can favour brood sex ratio adjustment, such as reduced maternal condition, food availability and partner attractiveness. Therefore, the steroid hormone has been suggested to play a key role in sex ratio manipulation. However, despite correlative and causal evidence CORT is linked to sex ratio manipulation in some avian species, the timing of adjustment varies between studies. Consequently, whether CORT is consistently involved in sex-ratio adjustment, and how the hormone acts as a mechanism for this adjustment remains unclear. Here we measured maternal baseline CORT and body condition in free-living blue tits (Cyanistes caeruleus) over three years and related these factors to brood sex ratio and nestling quality. In addition, a non-invasive technique was employed to experimentally elevate maternal CORT during egg laying, and its effects upon sex ratio and nestling quality were measured. We found that maternal CORT was not correlated with brood sex ratio, but mothers with elevated CORT fledged lighter offspring. Also, experimental elevation of maternal CORT did not influence brood sex ratio or nestling quality. In one year, mothers in superior body condition produced male biased broods, and maternal condition was positively correlated with both nestling mass and growth rate in all years. Unlike previous studies maternal condition was not correlated with maternal CORT. This study provides evidence that maternal condition is linked to brood sex ratio manipulation in blue tits. However, maternal baseline CORT may not be the mechanistic link between the maternal condition and sex ratio adjustment. Overall, this study serves to highlight the complexity of sex ratio adjustment in birds and the difficulties associated with identifying sex biasing mechanisms.     

Ready to Fight: Reliable Predictors of Attack in a Cooperatively Breeding,Non‐Passerine Bird

Signal reliability is a major focus of animal communication research. Aggressive signals are ideal for measuring signal reliability because the signal referent – attack or no attack – can be measured unambiguously. Signals of aggressive intent occur at elevated rates in aggressive contexts, predict subsequent aggression by the signaler, and elicit appropriate responses from receivers. We tested the ‘predictive criterion’ in smooth‐billed anis, Crotophaga ani, by broadcasting one of two playback types (‘ahnee’ calls only or ‘ahnee + hoot’ calls), presenting a taxidermic mount, and observing the animals’ behavior. Based on the hypotheses that ‘hoot’ calls and ‘throat‐inflation’ displays signal aggressive intent, we predicted that they would be associated with attack, and that signaling rate would increase over the time period leading up to an attack. Indeed, both hoots and throat‐inflation displays reliably predicted attack. The second prediction, that signaling rate increases in the time leading up to attack, was strongly supported for throat‐inflation displays, which increased over the pre‐attack period in both treatments. Hoots increased over the pre‐attack period in ahnee playbacks but not in ahnee + hoot playbacks. Hierarchical signaling systems are characterized by early, less‐reliable predictors of attack, and later, more reliable predictors of attack. During both natural and simulated interactions, the more‐reliable throat‐inflation display tended to precede the less‐reliable hoot call, suggesting that this signaling system is not hierarchical. In a comparison of 11 putative signals of aggressive intent in birds, the throat‐inflation display had the second highest mutual information (reduction in uncertainty) among visual signals and non‐passerine signals while hoots had below‐average mutual information. Natural observations indicate that both hoots and throat‐inflation displays occur in the context of aggressive between‐group encounters, and hoots also occur during within‐group interactions. Throat‐inflation displays appear to be reliable indicators of aggressive intent, but the function of hoot calls is less clear.     

Seasonally Changing Cryptochrome 1b Expression in the Retinal Ganglion Cells of a Migrating Passerine Bird

Cryptochromes, blue-light absorbing proteins involved in the circadian clock, have been proposed to be the receptor molecules of the avian magnetic compass. In birds, several cryptochromes occur: Cryptochrome 2, Cryptochrome 4 and two splice products of Cryptochrome 1, Cry1a and Cry1b. With an antibody not distinguishing between the two splice products, Cryptochrome 1 had been detected in the retinal ganglion cells of garden warblers during migration. A recent study located Cry1a in the outer segments of UV/V-cones in the retina of domestic chickens and European robins, another migratory species. Here we report the presence of cryptochrome 1b (eCry1b) in retinal ganglion cells and displaced ganglion cells of European Robins, Erithacus rubecula. Immuno-histochemistry at the light microscopic and electron microscopic level showed eCry1b in the cell plasma, free in the cytosol as well as bound to membranes. This is supported by immuno-blotting. However, this applies only to robins in the migratory state. After the end of the migratory phase, the amount of eCry1b was markedly reduced and hardly detectable. In robins, the amount of eCry1b in the retinal ganglion cells varies with season: it appears to be strongly expressed only during the migratory period when the birds show nocturnal migratory restlessness. Since the avian magnetic compass does not seem to be restricted to the migratory phase, this seasonal variation makes a role of eCry1b in magnetoreception rather unlikely. Rather, it could be involved in physiological processes controlling migratory restlessness and thus enabling birds to perform their nocturnal flights.     

Social Environment Affects Acquisition and Color of Structural Nuptial Plumage in a Sexually Dimorphic Tropical Passerine

Structural colors result from the physical interaction of light with organic materials of differing refractive indexes organized at nanoscale dimensions to produce significant interference effects. Because color properties emerge from these finely organized nanostructures, the production of structural coloration could respond to environmental factors and be developmentally more plastic than expected, functioning as an indicator of individual quality. However, there are many unknown factors concerning the function and mechanisms regulating structural coloration, especially relative to social environment. We hypothesized that social environment, in the form of competitive settings, can influence the developmental pathways involving production of feather structural coloration. We experimentally assessed the impact of social environment upon body condition, molt and spectral properties of two types of structural color that compose the nuptial plumage in blue-black grassquits: black iridescent plumage and white underwing patches. We manipulated male social environment during nine months by keeping individuals in three treatments: (1) pairs; (2) all-male groups; and (3) male-female mixed groups. All morphological characters and spectral plumage measures varied significantly through time, but only acquisition of nuptial plumage coverage and nuptial plumage color were influenced by social environment. Compared with males in the paired treatment, those in treatments with multiple males molted into nuptial plumage faster and earlier, and their plumage was more UV-purple-shifted. Our results provide experimental evidence that social context strongly influences development and expression of structural plumage. These results emphasize the importance of long-term experimental studies to identify the phenotypic consequences of social dynamics relative to ornament expression.     

A Scansorial Passerine Bird (Passeriformes,Certhioidea) from the Uppermost Lower Miocene of Eastern Siberia

A new scansorial passerine bird, Kischinskinia scandens gen. et sp. nov., from the uppermost Lower Miocene of the Tagay locality (Olkhon Island, Lake Baikal) is described based on a distal tarsometatarsal fragment. This is the first Asian member of the clade Certhioidea. A tibiotarsal fragment is also tentatively assigned to this taxon. Both bones display adaptations for climbing on a vertical surface. The find of a scansorial passerine bird of the clade Certhioidea is evidence of ecological similarity of Early Miocene avifaunas of southern Eastern Siberia and Western Europe, since a representative of Certhioidea showing a similar level of specialization was described from the Lower Miocene (MN3) of Germany. In addition, Kischinskinia scandens is the earliest reliable member of oscine passerines (Oscines) from Asia.     

The Process and Causes of Fledging in a Cavity-Nesting Passerine Bird, the House Wren (Troglodytes aedon)

Little is known about the process or causes of fledging or nest‐leaving in passerine birds because researchers can rarely predict when fledging will occur in a given nest. We used continuous videotaping of nests to both document the process of fledging in the house wren, Troglodytes aedon, a small, cavity‐nesting songbird, and test hypotheses as to what might cause fledging to begin. Fledging began any time from 14 to 19 d after hatching commenced. Slower‐developing broods fledged later than faster‐developing broods. Fledging typically began within 5 h of sunrise and over 80% of all nestlings fledged before noon. All nestlings fledged on the same day at 65% of nests and over two consecutive days in most other nests. We found no evidence that fledging was triggered by changes in parental behaviour. Parental rate of food delivery to nestlings did not decline during a 3‐h period leading up to the first fledging, nor was the rate of feeding just prior to the first fledging lower than the rate at the same time the day before. Moreover, parents did not slow the rate of food delivery to nests after part of the brood had fledged. Hatching is asynchronous in our study population which creates a marked age/size hierarchy within broods. At most nests, the first nestling to fledge was the most well‐developed nestling in the brood or nearly so (as measured by feather length). This suggests that fledging typically begins when the most well‐developed nestlings in the brood reach some threshold size. However, at about one‐fifth of nests, the first nestling to fledge was only moderate in size. At these nests, severe competition for food may have caused smaller, less competitive nestlings to fledge first to increase their access to food. We found no strong support for the suggestion that the oldest nestlings delay fledging until their least‐developed nestmate reaches some minimum size, although further experimental work on this question is warranted.     

Variation in Helper Type Affects Group Stability and Reproductive Decisions in a Cooperative Breeder

Recent studies have shown that differences in life history may lead to consistent inter‐individual variation in behavioural traits, so‐called behavioural syndromes, animal personalities or temperaments. Consistencies of behaviours and behavioural syndromes have mainly been studied in non‐cooperative species. Insights on the evolution of cooperation could be gained from studying individual differences in life histories and behavioural traits. Kin selection theory predicts that if an individual’s reproductive ability is low, it had to aim at gaining inclusive fitness benefits by helping others. We tested this prediction in the cooperatively breeding cichlid Neolamprologus pulcher, by assessing reproductive parameters of adults that had been tested earlier for aggressiveness and for their propensity to assist breeders when they had been young (‘juveniles’). We found that juvenile aggression levels predicted the acceptance of a subordinate in the group when adult. Males which were aggressive as juveniles were significantly more likely to tolerate a subordinate in the group when compared with males which were peaceful as juveniles, whereas females which were more aggressive as juveniles tended to expel subordinates more often. Females produced significantly smaller clutches when paired to males which had helped more as a juvenile, despite the fact that adult males hardly provided direct brood care. There was no evidence that females with a high propensity to help when young, produced smaller clutches or eggs when adult, but they took longer to lay their first clutch when compared with females with a low propensity to help when young. These results suggest that variation in behavioural types might explain variation in cooperation, the extent of group‐living and reproductive decisions.     

Do Primary Males Physiologically Suppress Subordinate Males? An Experiment in a Cooperatively Breeding Passerine

Knowing why certain individuals refrain from reproduction is fundamental to our understanding of the evolution of cooperative breeding. Although many studies have focused on the role of life history and ecological factors, the proximate mechanisms underlying this behaviour have received considerably less attention. We determined the natural variation in plasma testosterone (T) level and cloacal protuberance (CP) size – an indication of sperm storage – in successfully reproducing primary male and in reproductively inactive subordinate male Seychelles warblers ( Acrocephalus sechellensis ). Primary males had significantly higher T levels during female's fertile period and significantly larger CPs throughout the breeding season than subordinate males. To test if the lower T levels of subordinates were caused by their social status per se, we experimentally promoted subordinates to primary males, by permanent removal of primary males from their territories. The experimentally promoted males increased T production and CP sizes significantly, suggesting former suppression by primary males. However, T levels of the promoted males only marginally increased. As this could not be explained by their younger age, we conclude that recovery from social suppression may take a substantial time period.     

Relationships Between Vegetative and Life History Traits and Fitness in a Novel Field Environment: Impacts of Herbivores

At the edge of a species range, plants may experience myriad microenvironmental gradients, which may differ and impose strong yet complex selective regimes. We explore these issues using the model organism Arabidopsis thaliana, a native of Europe that has naturalized in North America, which we planted in a common garden field plot in Knoxville, Tennessee and observed across two biotic gradients. We found evidence that directional selection favors increased plant size, consistent with hypotheses of plant responses to novel environments. However, selection differed among plants with fungus gnat larvae damage, aphid damage, and plants that escaped herbivory, evidence that the selective landscape is variable and complex even for quasi-natural field plots. We did not uncover evidence for resistance; however, our results suggest that tolerance of A. thaliana may play an important role for population establishment and persistence in the presence of herbivores in a novel environment. Our findings highlight the variation in one segment of the biotic selective landscape of field environments, as well as the importance of biotic interactions in shaping the success of recently established populations that may be a critical component of post-invasion evolution.