Testing the phenotype‐linked fertility hypothesis in the presence and absence of inbreeding

The phenotype‐linked fertility hypothesis suggests that females can judge male fertility by inspecting male phenotypic traits. This is because male sexually selected traits might correlate with sperm quality if both are sensitive to factors that influence male condition. A recent meta‐analysis found little support for this hypothesis, suggesting little or no shared condition dependence. However, we recently reported that in captive zebra finches (Taeniopygia guttata) inbreeding had detrimental effects both on phenotypic traits and on measures of sperm quality, implying that variation in inbreeding could induce positive covariance between indicator traits and sperm quality. Therefore, we here assess empirically the average strength of correlations between phenotypic traits (courtship rate, beak colour, tarsus length) and measures of sperm quality (proportion of functional sperm, sperm velocity, sperm length) in populations of only outbred individuals and in mixed populations consisting of inbreds (F = 0.25) and outbreds (F = 0). As expected, phenotype sperm‐trait correlations were stronger when the population contained a mix of inbred and outbred individuals. We also found unexpected heterogeneity between our two study populations, with correlations being considerably stronger in a domesticated population than in a recently wild‐derived population. Correlations ranged from essentially zero among outbred‐only wild‐derived birds (mean Fisher's Zr ± SE = 0.03 ± 0.10) to moderately strong among domesticated birds of mixed inbreeding status (Zr ± SE = 0.38 ± 0.08). Our results suggest that, under some conditions, the phenotype‐linked fertility hypothesis might apply.     

Testing inflated zeros in binomial regression models

Binomial regression models are commonly applied to proportion data such as those relating to the mortality and infection rates of diseases. However, it is often the case that the responses may exhibit excessive zeros; in such cases a zero‐inflated binomial (ZIB) regression model can be applied instead. In practice, it is essential to test if there are excessive zeros in the outcome to help choose an appropriate model. The binomial models can yield biased inference if there are excessive zeros, while ZIB models may be unnecessarily complex and hard to interpret, and even face convergence issues, if there are no excessive zeros. In this paper, we develop a new test for testing zero inflation in binomial regression models by directly comparing the amount of observed zeros with what would be expected under the binomial regression model. A closed form of the test statistic, as well as the asymptotic properties of the test, is derived based on estimating equations. Our systematic simulation studies show that the new test performs very well in most cases, and outperforms the classical Wald, likelihood ratio, and score tests, especially in controlling type I errors. Two real data examples are also included for illustrative purpose.     

Feed‐backs among inbreeding,inbreeding depression in sperm traits,and sperm competition can drive evolution of costly polyandry

Ongoing ambitions are to understand the evolution of costly polyandry and its consequences for species ecology and evolution. Emerging patterns could stem from feed‐back dynamics between the evolving mating system and its genetic environment, defined by interactions among kin including inbreeding. However, such feed‐backs are rarely considered in nonselfing systems. We use a genetically explicit model to demonstrate a mechanism by which inbreeding depression can select for polyandry to mitigate the negative consequences of mating with inbred males, rather than to avoid inbreeding, and to elucidate underlying feed‐backs. Specifically, given inbreeding depression in sperm traits, costly polyandry evolved to ensure female fertility, without requiring explicit inbreeding avoidance. Resulting sperm competition caused evolution of sperm traits and further mitigated the negative effect of inbreeding depression on female fertility. The evolving mating system fed back to decrease population‐wide homozygosity, and hence inbreeding. However, the net overall decrease was small due to compound effects on the variances in sex‐specific reproductive success and paternity skew. Purging of deleterious mutations did not eliminate inbreeding depression in sperm traits or hence selection for polyandry. Overall, our model illustrates that polyandry evolution, both directly and through sperm competition, might facilitate evolutionary rescue for populations experiencing sudden increases in inbreeding.     

Lack of effects on male fertility from a quadrivalent HPV vaccine in Sprague‐Dawley rats

BACKGROUND: Human papillomavirus (HPV) infection is one of the most common sexually transmitted diseases in both men and women. A recently developed quadrivalent HPV vaccine, Gardasil^®, has been shown to be highly effective in the prevention of several HPV‐mediated diseases. The objective of the present study was to evaluate the potential effects of the vaccine on male fertility including reproductive performance, sperm evaluations, and histology of the testes. In addition, anti‐HPV antibodies were measured during the study. METHODS: Group 1 (30 male rats) received the full human dose of vaccine (0.5 mL, ～200‐fold excess based on body weight) by intramuscular injection at 6 weeks, 3 weeks, and 3 days prior to cohabitation. Group 2 males received only 1 dose at 3 days prior to cohabitation. Additional groups (20 male rats each) were administered PBS or Merck Aluminum Adjuvant similarly to Group 1. Ten males in the vaccine‐treated groups were bled for immunogenicity assays after each dose. Twenty males per group were mated to untreated female rats. Cesarean sections were performed on Gestation Day 15 or 16. Cohabited males were necropsied and sperm count and motility were evaluated. RESULTS: There were no unscheduled deaths during the study and no evidence of toxicity in vaccine‐treated male rats. The vaccine induced a specific antibody response to the 4 HPV types after each injection. There were no effects on the cesarean‐section parameters of females or reproductive parameters of the cohabited male rats, including histomorphology of testes and epididymis, sperm count, and sperm motility. CONCLUSIONS: These results demonstrate that this quadrivalent HPV vaccine had no detectable adverse effects on routine measures of male fertility in rats. Birth Defects Res (Part B) 89:376–381, 2010. © 2010 Wiley‐Liss, Inc.     

高等植物胞质雄性不育及育性恢复的分子生物学研究进展

综述了几种植物胞质雄性不育的分子机理研究进展,着重介绍了与细胞质雄性不育相关的线粒体连锁位点的分析及育性恢复的几种假说,并对今后的研究进行了讨论。     

The effects of inbreeding and heat stress on male sterility in Drosophila melanogaster

Understanding the consequences of inbreeding in combination with stress is important for the persistence of small endangered populations in a changing environment. Inbreeding and stress can influence the population at all stages of the life cycle, and in the last two decades a number of studies have demonstrated inbreeding depression for most life‐cycle components, both in laboratory populations and in the wild. Although male fertility is known to be sensitive to temperature extremes, few studies have focused on this life‐cycle component. We studied the effects of inbreeding on male sterility in benign and stressful environments using Drosophila melanogaster as a model organism. Male sterility was compared in 21 inbred lines and five non‐inbred control lines at 25.0 and 29.0 °C. The effect of inbreeding on sterility was significant only at 29.0 °C. This stress‐induced increase in sterility indicates an interaction between the effects of inbreeding and high‐temperature stress on male sterility. In addition, the stress‐induced temporary and permanent sterility showed significant positive correlation, as did stress‐induced sterility and the decrease in egg‐to‐adult viability. This suggests that the observed stress‐induced decline in fitness could result from conditionally expressed, recessive deleterious alleles affecting both sterility and viability simultaneously. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 432–442.     

Littoral habitat loss caused by multiyear drought and the response of an endemic fish species in a deep desert lake

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温敏不育系A3314在中国不同生态地点的育性表现

利用作者参与发明的ZL00105488．0专利方法选育的小麦温度敏感不育系A3314在中国元谋、杨陵、石家庄、互助、依安、贵阳、武威7个不同纬度地点种植的自交结实率,结合各点光温条件的分析表明：A3314在黄淮冬麦区、云贵冬麦区、西北春麦区、东北春麦区各点,按当地小麦生产正季播种均表现稳定雄性不育;而在黄淮和云贵冬麦区春播(夏播)则自交结实,适宜条件下自交结实率可达60％以上。说明该温敏不育系的雄性育性受温度的制约,而与日长无明显相关。根据A3314的育性表现,推测它在中国大部分小麦产区均可安全用于杂交小麦制种。     

Estimating plant abundance using inflated beta distributions: Applied learnings from a lichen–caribou ecosystem

Quantifying abundance and distribution of plant species can be difficult because data are often inflated with zero values due to rarity or absence from many ecosystems. Terrestrial fruticose lichens (Cladonia and Cetraria spp.) occupy a narrow ecological niche and have been linked to the diets of declining caribou and reindeer populations (Rangifer tarandus) across their global distribution, and conditions related to their abundance and distribution are not well understood. We attempted to measure effects related to the occupancy and abundance of terrestrial fruticose lichens by sampling and simultaneously modeling two discrete conditions: absence and abundance. We sampled the proportion cover of terrestrial lichens at 438 vegetation plots, including 98 plots having zero lichens. A zero‐inflated beta regression model was employed to simultaneously estimate both the absence and the proportion cover of terrestrial fruticose lichens using fine resolution satellite imagery and light detection and ranging (LiDAR) derived covariates. The probability of lichen absence significantly increased with shallower groundwater, taller vegetation, and increased Sphagnum moss cover. Vegetation productivity, Sphagnum moss cover, and seasonal changes in photosynthetic capacity were negatively related to the abundances of terrestrial lichens. Inflated beta regression reliably estimated the abundance of terrestrial lichens (R² = .74) which was interpolated on a map at fine resolution across a caribou range to support ecological conservation and reclamation. Results demonstrate that sampling for and simultaneously estimating both occupancy and abundance offer a powerful approach to improve statistical estimation and expand ecological inference in an applied setting. Learnings are broadly applicable to studying species that are rare, occupy narrow niches, or where the response variable is a proportion value containing zero or one, which is typical of vegetation cover data.     

玉米CMS-C同质异核不育系育性恢复的遗传研究

玉米是最早利用细胞质雄性不育系生产杂交种的作物之一,C型细胞质雄性不育系（C-type cytoplasmic male sterile, CMS-C）在杂交种生产中具有重要的作用,育性恢复的稳定性直接影响其应用价值。然而,玉米CMS-C的育性恢复机理复杂,且至今仍不明确。为进一步探究玉米CMS-C育性恢复的影响因素,本研究以玉米CMS-C同质异核不育系C48-2、C黄早四和C478为母本,分别与测验系18白、自330、5022以及恢复系A619组配杂交获得F₁。其中育性恢复F₁通过自交获得F₂,并以育性恢复F₁为父本分别给育性保持F₁授粉,组配双交群体,共获得4个F₂群体,6个双交群体。同时以不育系C48-2、C黄早四和C478为母本,各自的保持系48-2、黄早四和478为父本杂交组配不完全双列杂交F₁。将所有杂交组合的F₁、F₂以及双交组合群体分别在不同年份不同地点种植观察,通过植株田间育性调查并结合室内花粉镜检鉴定育性表现。结果表明：1) 同一测验系对玉米CMS-C同质异核不育系的恢保关系不同,暗示不育系的核背景参与调控育性恢复表现;2) 在不同年份不同地点对(C48-2×A619) F₂群体进行种植观察,发现不同环境下F₂群体可育株与不育株的分离比均符合15∶1,但在云南种植的可育株的育性级别主要为Ⅲ和Ⅳ级,而在四川种植的可育株的育性级别主要为Ⅴ级,表明环境对恢复系A619恢复后代的育性表现有影响;3) 通过恢保关系测定发现18白不能恢复C478,48-2也不能恢复C478,但双交群体[(C478×18白) F_1S×(C48-2×18白) F_1F]后代却出现了可育株与不育株的分离;同理,双交群体[(C48-2×自330) F_1S×(C478×自330) F_1F]的后代也出现了可育株与不育株的分离。因此,本文推测C48-2、C478核背景中存在微效恢复基因,这些微效基因与18白、自330中的微效恢复基因通过杂交聚合后能使C478、C48-2的育性恢复,暗示玉米CMS-C的育性恢复呈现一定的剂量效应。这些结果为进一步认识玉米CMS-C育性恢复的复杂性和多样性奠定了基础,为深入研究玉米CMS-C育性恢复机理以及加快CMS-C在不育化制种中的应用提供重要参考。     

Homozygosity at a class II MHC locus depresses female reproductive ability in European brown hares

The link between adaptive genetic variation, individual fitness and wildlife population dynamics is fundamental to the study of ecology and evolutionary biology. In this study, a Bayesian modelling approach was employed to examine whether individual variability at two major histocompatibility complex (MHC) class II loci (DQA and DRB) and eight neutral microsatellite loci explained variation in female reproductive success for wild populations of European brown hare (Lepus europaeus). We examined two aspects of reproduction: the ability to reproduce (sterility) and the number of offspring produced (fecundity). Samples were collected from eastern Austria, experiencing a sub‐continental climatic regime, and from Belgium with a more Atlantic‐influenced climate. As expected, reproductive success (both sterility and fecundity) was significantly influenced by age regardless of sampling locality. For Belgium, there was also a significant effect of DQA heterozygosity in determining whether females were able to reproduce (95% highest posterior density interval of the regression parameter [−3.64, −0.52]), but no corresponding effect was found for Austria. In neither region was reproduction significantly associated with heterozygosity at the DRB locus. DQA heterozygotes from both regions also showed a clear tendency, but not significantly so, to produce a larger number of offspring. Predictive simulations showed that, in Belgium, sub‐populations of homozygotes will have higher rates of sterile individuals and lower average offspring numbers than heterozygotes. No similar effect is predicted for Austria. The mechanism for the spatial MHC effect is likely to be connected to mate choice for increased heterozygosity or to the linkage of certain MHC alleles with lethal recessives at other loci.     

Normal fertility in male mice with deletion of β‐catenin gene in germ cells

As a dual function protein, β‐catenin affects both cell adhesion and mediates canonical Wnt/β‐catenin cell signaling. β‐Catenin is prominently expressed in somatic Sertoli cells in the testis and postmeiotic germ cells, suggesting an additional role in spermatogenesis. It was reported previously that Cre/loxP‐mediated conditional inactivation of the β‐catenin gene (Ctnnb1) in male gonads using a protamine promoter‐driven Cre transgene (Prm‐cre) resulted in partial infertility, reduced sperm count, and abnormal spermatogenesis. In this report, we demonstrated that the conditional deletion of Ctnnb1 using a germ cell specific Cre transgene (Stra8‐icre) had no effect on male fertility. We have shown that the Stra8‐icre transgene was highly efficient in generating deletion in early pre‐meiotic and post‐meiotic cells. No differences in anatomical or histological presentation were found in the mutant testis, the production of viable sperm was similar, and no abnormalities in DNA sperm content were detected. We concluded that β‐catenin is fully dispensable in germ cells for spermatogenesis. The conflicting results from the earlier study may have been due to off‐target expression of Prm‐cre in testicular somatic cells. In future studies, the analysis of conditional mutants using several Cre‐transgenes should be encouraged to reduce potential errors. genesis 52:328–332, 2014. © 2014 Wiley Periodicals, Inc.     

Analysis of the effects of early nutritional environment on inbreeding depression in Drosophila melanogaster

The impact of nutritional deficiencies early in life in determining life-history variation in organisms is well recognized. The negative effects of inbreeding on fitness are also well known. Contrary to studies on vertebrates, studies on invertebrates are not consistent with the observation that inbreeding compromises resistance to parasites and pathogens. In this study, we investigated the effect of early nutrition on the magnitude of inbreeding depression in development time, adult body size and adult resistance to the bacterium Serratia marcescens in Drosophila melanogaster. We found that early nutritional environment had no effect on the magnitude of inbreeding depression in development time or adult body size but may have played a small role in adult resistance to the bacterial infection. Estimates of heritabilities for development time under the poor nutritional environment were larger than those measured under the standard nutritional conditions.     

Expanding northward: influence of climate change,forest connectivity,and population processes on a threatened species' range shift

Species' ranges are dynamic, shifting in response to a large number of interrelated ecological and anthropogenic processes. Climate change is thought to be one of the most influential drivers of range shifts, but the effects of other confounded ecological processes are often ignored even though these processes may modify expected range responses to climate change. To determine the relative effects of climate, forest availability, connectivity, and biotic processes such as immigration and establishment, we examine range changes occurring in a species of bird, the Hooded Warbler (Wilsonia citrina). We focus predominantly on the periphery of the species' northern range in Canada but we also examine data from the entire species' range. Nesting records in southern Ontario were obtained from two breeding bird Atlases of Ontario separated by a period of 20 years (1981–1985 and 2001–2005), and the rate of range expansion was estimated by comparing the number of occupied areas in each Atlas. Twelve hypotheses of the relationship between the rate of range expansion and factors known to influence range change were examined using model‐selection techniques and a mixed modeling approach (zero‐inflated Poisson's regression). Cooler temperatures were positively related to a lack of range expansion indicating that climate constrained the species' distribution. Establishment probability (based on the number of occupied, neighboring Atlas squares) and immigration from populations to the south (estimated using independent data from the North American Breeding Bird Survey) were also important predictors of range expansion. These biotic process variables can mask the effects of forest availability and connectivity on range expansion. Expansion due to climate change may be slower in fragmented systems, but the rate of expansion will be influenced largely by biotic processes such as proximity to neighboring populations.     

Epidermal jasmonate perception is sufficient for all aspects of jasmonate‐mediated male fertility in Arabidopsis

Jasmonate (JA) signaling is essential for several environmental responses and reproductive development in many plant species. In Arabidopsis thaliana, the most obvious phenotype of JA biosynthetic and perception mutants is profound sporophytic male sterility characterized by failure of stamen filament elongation, severe delay of anther dehiscence and pollen inviability. The site of action of JA in the context of reproductive development has been discussed, but the ideas have not been tested experimentally. To this end we used targeted expression of a COI1‐YFP transgene in the coi1‐1 mutant background. As COI1 is an essential component of the JA co‐receptor complex, the null coi1‐1 mutant is male sterile due to lack of JA perception. We show that expression of COI1‐YFP in the epidermis of the stamen filament and anther in coi1 mutant plants is sufficient to rescue filament elongation, anther dehiscence and pollen viability. In contrast, filament expression alone or expression in the tapetum do not restore dehiscence and pollen viability. These results demonstrate that epidermal JA perception is sufficient for anther function and pollen viability, and suggest the presence of a JA‐dependent non‐autonomous signal produced in the anther epidermis to synchronize both anther dehiscence and pollen maturation.     

Choosing the right sigmoid growth function using the unified‐models approach

Growth of the young is an important part of the life history in birds. However, modelling methods have paid little attention to the choice of regression model used to describe its pattern. The aim of this study was to evaluate whether a single sigmoid model with an upper asymptote could describe avian growth adequately. We compared unified versions of five growth models of the Richards family (the four‐parameter U‐Richards and the three‐parameter U‐logistic, U‐Gompertz, U‐Bertalanffy and U4‐models) for three traits (body mass, tarsus‐length and wing‐length) for 50 passerine species, including species with varied morphologies and life histories. The U‐family models exhibit a unified set of parameters for all models. The four‐parameter U‐Richards model proved a good choice for fitting growth curves to various traits – its extra d‐parameter allows for a flexible placement of the inflection point. Which of the three‐parameter U‐models was the best performing varied greatly between species and between traits, as each three‐parameter model had a different fixed relative inflection value (fraction of the upper asymptote), implying a different growth pattern. Fixing the asymptotes to averages for adult trait value generally shifted the model preference towards one with lower relative inflection values. Our results illustrate an overlooked difficulty in the analysis of organismal growth, namely, that a single traditional three‐parameter model does not suit all growth data. This is mostly due to differences in inflection placement. Moreover, some biometric traits require more attention when estimating growth rates and other growth‐curve characteristics. We recommend fitting either several three‐parameter models from the U‐family, where the parameters are comparable between models, or only the U‐Richards model.     

Partitioning the sources of demographic variation reveals density‐dependent nest predation in an island bird population

Ecological factors often shape demography through multiple mechanisms, making it difficult to identify the sources of demographic variation. In particular, conspecific density can influence both the strength of competition and the predation rate, but density‐dependent competition has received more attention, particularly among terrestrial vertebrates and in island populations. A better understanding of how both competition and predation contribute to density‐dependent variation in fecundity can be gained by partitioning the effects of density on offspring number from its effects on reproductive failure, while also evaluating how biotic and abiotic factors jointly shape demography. We examined the effects of population density and precipitation on fecundity, nest survival, and adult survival in an insular population of orange‐crowned warblers (Oreothlypis celata) that breeds at high densities and exhibits a suite of traits suggesting strong intraspecific competition. Breeding density had a negative influence on fecundity, but it acted by increasing the probability of reproductive failure through nest predation, rather than through competition, which was predicted to reduce the number of offspring produced by successful individuals. Our results demonstrate that density‐dependent nest predation can underlie the relationship between population density and fecundity even in a high‐density, insular population where intraspecific competition should be strong.