Maternal Testosterone and Offspring Sex-Ratio in Birds and Mammals: A Meta-Analysis

Sex allocation theory predicts that parents should bias offspring sex to maximize their fitness in a given context. Quantifying the fitness benefits of offspring sex-ratio biases would be facilitated by a better knowledge of their underlying mechanism(s) and associated costs. The hypothesis that steroid hormones are involved in sex determination has gained in popularity recently. Being influenced by external stimuli and involved in a range of physiological processes, they could be a ubiquitous mediator of environmental conditions influencing sex-ratio with low fitness costs. Previous studies indicated that higher maternal testosterone levels led to the overproduction of sons around conception in both birds and mammals. We conducted a systematic review (including meta-analysis) of these studies and, as predicted, we found a weak positive and significant overall effect of maternal testosterone on the proportion of sons. Neither taxa, nor the type of study (experimental/observational), or the timing of timing testosterone manipulation/measure were significant predictors of offspring sex-ratio, which may be explained by low statistical power in addition to low variability between effect sizes. Our meta-analysis provides evidence for a general positive influence of maternal testosterone around conception on the proportion of sons across birds and mammals, although less confidently so for the latter. It begs for more large-scale experimental studies, especially on mammals, and ideally in the wild. It may also have some important consequences for the poultry industry.     

Local Competition, Inbreeding, and the Evolution of Sex-Biased Dispersal

Using game theory, we developed a kin-selection model to investigate the consequences of local competition and inbreeding depression on the evolution of natal dispersal. Mating systems have the potential to favor strong sex biases in dispersal because sex differences in potential reproductive success affect the balance between local resource competition and local mate competition. No bias is expected when local competition equally affects males and females, as happens in monogamous systems and also in polygynous or promiscuous ones as long as female fitness is limited by extrinsic factors (breeding resources). In contrast, a male-biased dispersal is predicted when local mate competition exceeds local resource competition, as happens under polygyny/promiscuity when female fitness is limited by intrinsic factors (maximal rate of processing resources rather than resources themselves). This bias is reinforced by among-sex interactions: female philopatry enhances breeding opportunities for related males, while male dispersal decreases the chances that related females will inbreed. These results meet empirical patterns in mammals: polygynous/promiscuous species usually display a male-biased dispersal, while both sexes disperse in monogamous species. A parallel is drawn with sex-ratio theory, which also predicts biases toward the sex that suffers less from local competition. Optimal sex ratios and optimal sex-specific dispersal show mutual dependence, which argues for the development of coevolution models.     

Sex-Biased Dispersal at Different Geographical Scales in a Cooperative Breeder from Fragmented Rainforest

Dispersal affects both social behavior and population structure and is therefore a key determinant of long-term population persistence. However, dispersal strategies and responses to spatial habitat alteration may differ between sexes. Here we analyzed spatial and temporal variation in ten polymorphic microsatellite DNA loci of male and female Cabanis’s greenbuls ( Phyllastrephus cabanisi ), a cooperative breeder of Afrotropical rainforest, to quantify rates of gene flow and fine-grained genetic structuring within and among fragmented populations. We found genetic evidence for female-biased dispersal at small spatial scales, but not at the landscape level. Local autocorrelation analysis provided evidence of positive genetic structure within 300 m distance ranges, which is consistent with behavioral observations of short-distance natal dispersal. At a landscape scale, individual-based autocorrelation values decreased over time while levels of admixture increased, possibly indicating increased gene flow over the past decade.     

Chlorpyrifos: Ecotoxicological Risk Assessment for Birds and Mammals in Corn Agroecosystems

A tiered risk assessment was conducted for the use of granular and liquid formulations of chlorpyrifos in corn agroecosystems in the U.S. The initial screening Tier I assessment suggested that under high-exposure scenarios the granular and some spray formulations present potential hazards to birds. Higher tiered probabilistic risk assessments were conducted separately for the granular and liquid formulations. The probabilistic assessment indicated that risk to birds from exposure to granular formulation is small and that this route of exposure would not be a significant source of mortality. Similarly, the assessment of potential exposure of birds to food items contaminated with chlorpyrifos showed that the risk from exposure via food was small, even if it was assumed that birds feed only on the treated fields. Although they have potentially greater sensitivity to chlorpyrifos, effects in nestling birds consuming food items from fields treated with granular chlorpyrifos were negligible. However, risks to young birds may be greater where the major source of food is from fields treated with liquid formulations of chlorpyrifos. A review of field studies showed that wildlife mortality incidents associated with use of either granular or liquid formulations of chlorpyrifos are not widely apparent in agroecosystems. Based on the multiple lines of evidence, we conclude that the presumption that chlorpyrifos use in corn agroecosystems will result in extensive mortality of terrestrial wildlife, particularly birds and mammals, is not supported by the scientific evidence.     

Gastrointestinal Bacteria of Certain Antarctic Birds and Mammals

An investigation was carried out of the aerobic gram-negative intestinal flora of 158 penguins, 30 skuas, and 66 seals from the Antarctic and sub-Antarctic zones and Phillip Island. Among penguins and seals, 17% and 11%, respectively, were devoid of aerobic enteric organisms, but microscopic examination showed the presence of other bacteria. The coliforms outnumbered the paracolons and nonlactosefermenting bacteria; irregular coliform types and Escherichia coli were predominant. The present study indicated the effect of diet on the composition of the intestinal flora of the birds and mammals examined.     

Stepparental Behavior as Mating Effort in Birds and Other Animals

In many animal species, widowed or divorced parents may remate before young of the prior union are independent. In such circumstances, stepparents may kill their predecessors' offspring, may tolerate them without providing care, or may invest in them more or less as genetic parents do. Rohwer proposed that all three of these responses may be understood as mating tactics, adapted to different social and ecological circumstances. We discuss the selection pressures that would favor each of these alternatives and review relevant evidence on nonhuman stepparenting, especially in birds. Stepparental tolerance and (partial or full) care, which are the predominant human responses, are common in nonhuman animals too, and in many cases there is evidence supporting their interpretation as stepparental mating effort adaptations. In general, however, this interpretation is not as well established for tolerance and care as it is for stepparental infanticide. Because tolerance and care are not distinct modes of behavior peculiar to stepparents, the hypothesis that they are nonadaptive by-products of parental psychology often remains tenable. We discuss the kinds of evidence needed to choose between by-product and stepparental adaptation hypotheses.     

Identifying Environmental Determinants of Diurnal Distribution in Marine Birds and Mammals

Marine birds and mammals move between various habitats during the day as they engage in behaviors related to resting, sleeping, preening, feeding, and breeding. The per capita rates of movement between these habitats, and hence the habitat occupancy dynamics, often are functions of environmental variables such as tide height, solar elevation, wind speed, and temperature. If the system recovers rapidly after disturbance, differential equation models of occupancy dynamics can be reduced to algebraic equations on two time scales. Identification of environmental factors that influence movement between habitats requires time series census data collected in both the absence and presence of disturbance.     

Comparative Biochemistry of the Pineal Glands of Birds and Mammals

Melatonin is synthesized from serotonin in the pineal glandby N-acetyltransferase and hydroxyindole-O-methyltransferase(HIOMT). The activities of these two enzymes have been comparedin the pineal glands of rats, hamsters, chickens, and sparrows.Three different patterns of pineal biochemistry have been observedin the four species. Evidence for the regulation of pineal N-acetyltransferaseactivity by a noradrenergic system exists in rats but not inchickens, hamsters, and sparrows.     

Competition Among Insects, Birds and Mammals for Conifer Steeds

Species of at least 5 orders of insects, 6 families of birds,and 2 orders of mammals, in various combinations, can exploitthe cones and seeds of most species of conifers. Lodgepole pineis the exception to this pattern of broad taxonomic diversityof seed predators in that only pine squirrels and coreid bugsattack its serotinous cones. The contrast between lodgepolepine and other conifers demonstrates that large intrinsic variationin the abundance of a resource fosters the evolution of a broadrange of taxonomic groups to exploit the resource. The diversegroups'are limited by different predators and alternate resourceswhen conifer seeds independently decrease in abundance.     

Independent Evolution of Transcriptional Inactivation on Sex Chromosomes in Birds and Mammals

X chromosome inactivation in eutherian mammals has been thought to be tightly controlled, as expected from a mechanism that compensates for the different dosage of X-borne genes in XX females and XY males. However, many X genes escape inactivation in humans, inactivation of the X in marsupials is partial, and the unrelated sex chromosomes of monotreme mammals have incomplete and gene-specific inactivation of X-linked genes. The bird ZW sex chromosome system represents a third independently evolved amniote sex chromosome system with dosage compensation, albeit partial and gene-specific, via an unknown mechanism (i.e. upregulation of the single Z in females, down regulation of one or both Zs in males, or a combination). We used RNA-fluorescent in situ hybridization (RNA-FISH) to demonstrate, on individual fibroblast cells, inactivation of 11 genes on the chicken Z and 28 genes on the X chromosomes of platypus. Each gene displayed a reproducible frequency of 1Z/1X-active and 2Z/2X-active cells in the homogametic sex. Our results indicate that the probability of inactivation is controlled on a gene-by-gene basis (or small domains) on the chicken Z and platypus X chromosomes. This regulatory mechanism must have been exapted independently to the non-homologous sex chromosomes in birds and mammals in response to an over-expressed Z or X in the homogametic sex, highlighting the universal importance that (at least partial) silencing plays in the evolution on amniote dosage compensation and, therefore, the differentiation of sex chromosomes.     

Parental Care: The Key to Understanding Endothermy and Other Convergent Features in Birds and Mammals

Birds and mammals share a number of features that are remarkably similar but that have evolved independently. One of these characters, endothermy, has been suggested to have played a cardinal role in avian and mammalian evolution. I hypothesize that it is parental care, rather than endothermy, that is the key to understanding the amazing convergence between mammals and birds. Endothermy may have arisen as a consequence of selection for parental care because endothermy enables a parent to control incubation temperature. The remarkable ability of many birds and mammals to sustain vigorous exercise may also have arisen as a consequence of selection for parental care because provisioning of offspring often requires sustained vigorous exercise. Because extensive parental care encompasses a wide range of behaviors, morphology, and physiology, it may be a key innovation that accounts for the majority of convergent avian and mammalian characters.     

Heterogeneity of Glia in the Retina and Optic Nerve of Birds and Mammals

We have recently described a novel type of glial cell that is scattered across the inner layers of the avian retina [1]. These cells are stimulated by insulin-like growth factor 1 (IGF1) to proliferate, migrate distally into the retina, and up-regulate the nestin-related intermediate filament transitin. These changes in glial activity correspond with increased susceptibility of neurons to excitotoxic damage. This novel cell-type has been termed the Non-astrocytic Inner Retinal Glia-like (NIRG) cells. The purpose of the study was to investigate whether the retinas of non-avian species contain cells that resemble NIRG cells. We assayed for NIRG cells by probing for the expression of Sox2, Sox9, Nkx2.2, vimentin and nestin. NIRG cells were distinguished from astrocytes by a lack of expression for Glial Fibrilliary Acidic Protein (GFAP). We examined the retinas of adult mice, guinea pigs, dogs and monkeys (Macaca fasicularis). In the mouse retina and optic nerve head, we identified numerous astrocytes that expressed GFAP, S100β, Sox2 and Sox9; however, we found no evidence for NIRG-like cells that were positive for Nkx2.2, nestin, and negative for GFAP. In the guinea pig retina, we did not find astrocytes or NIRG cells in the retina, whereas we identified astrocytes in the optic nerve. In the eyes of dogs and monkeys, we found astrocytes and NIRG-like cells scattered across inner layers of the retina and within the optic nerve. We conclude that NIRG-like cells are present in the retinas of canines and non-human primates, whereas the retinas of mice and guinea pigs do not contain NIRG cells.     

Social Spacing in Small Mammals: Patterns of Individual Variation

The pattern of social spacing in small mammals differs fromthat observed in many other vertebrates. Small mammals frequentlyhave non-exclusive territories and tolerate a large amount ofoverlap with other conspecifics. The determinant factors ofhome range or territory size in small mammals are not knownfor most species. We carried out a study of the determinantfactors of home range size in a model small mammal, the easternchipmunk, Tamias striatus. The population was studied for fiveyears. The effect of experimental perturbations on food supplyand population density offered strong evidence that the meanhome range size in the population was determined by resourceabundance. Changes in population density had little or no measurableeffect. We noted that even when mean home range size decreasedsignificantly in response to an increase in available food,a great deal of variability in individual home range sizes remained.We hypothesized that this pattern of variation among individualswas also resource related; large home ranges would be locatedin areas of low resource density and small home ranges wouldbe located in areas of high resource density. Our data to datedo not offer support for this hypothesis; however our researchhas shown that the data needed to convincingly reject the nullhypothesis are very complex. We discuss the evidence requiredto study patterns of individual variation, and how models ofoptimal territory size may be useful. Research that examinespatterns of individual variation are few in number, yet studiesof individual variation will ultimately provide the best insightson the dynamics of evolutionary ecology.     

陕西屋梁山自然保护区鸟兽物种多样性初步研究

2005年对秦岭西段南坡的屋梁山自然保护区的鸟兽物种多样性进行了初步调查.在保护区内发现有166种鸟类和68种兽类.其中29种是中国特有种,37种是国家重点保护动物,21种鸟兽具有灭绝风险.在区系组成方面,南方动物区系占有优势,但鸟类的过渡性特征更明显.根据海拔和生境划分的三个垂直分布带,每个分布带鸟兽的多样性组成都不相同.基于对鸟兽物种多样性的评价,表明屋梁山保护区具有较高的保护价值.     

Why Threonine Is an Essential Amino Acid in Mammals and Birds: Studies at the Enzyme Level

The only pathway for the synthesis of essential amino acids in vertebrates is reversible transamination of their keto analogs with glutamic acid. At the same time, it is commonly accepted that such essential amino acids as lysine and threonine are not involved in transamination and, therefore, cannot be synthesized from their keto analogs. However, using radio-labeled isotopes, synthesis of threonine was demonstrated in rat liver and in a reaction mixture containing chicken liver threonine dehydrogenase. In the review, we discuss why threonine is an essential amino acid in mammals and birds based on the pathways of threonine biosynthesis in these two classes of vertebrates.     

Multiple-Geographic-Scale Genetic Structure of Two Mangrove Tree Species: The Roles of Mating System,Hybridization, Limited Dispersal and Extrinsic Factors

Mangrove plants comprise a unique group of organisms that grow within the intertidal zones of tropical and subtropical regions and whose distributions are influenced by both biotic and abiotic factors. To understand how these extrinsic and intrinsic processes influence a more fundamental level of the biological hierarchy of mangroves, we studied the genetic diversity of two Neotropical mangrove trees, Avicenniagerminans and A. schaueriana, using microsatellites markers. As reported for other sea-dispersed species, there was a strong differentiation between A. germinans and A. schaueriana populations sampled north and south of the northeastern extremity of South America, likely due to the influence of marine superficial currents. Moreover, we observed fine-scale genetic structures even when no obvious physical barriers were present, indicating pollen and propagule dispersal limitation, which could be explained by isolation-by-distance coupled with mating system differences. We report the first evidence of ongoing hybridization between Avicennia species and that these hybrids are fertile, although this interspecific crossing has not contributed to an increase in the genetic diversity the populations where A. germinans and A. schaueriana hybridize. These findings highlight the complex interplay between intrinsic and extrinsic factors that shape the distribution of the genetic diversity in these sea-dispersed colonizer species.