Why What Juveniles Do Matters in the Evolution of Cooperative Breeding

The evolution of cooperative breeding is complex, and particularly so in humans because many other life history traits likely evolved at the same time. While cooperative childrearing is often presumed ancient, the transition from maternal self-reliance to dependence on allocare leaves no known empirical record. In this paper, an exploratory model is developed that incorporates probable evolutionary changes in birth intervals, juvenile dependence, and dispersal age to predict under what life history conditions mothers are unable to raise children without adult cooperation. The model’s outcome variable (net balance) integrates dependent children’s production and consumption as a function of varying life history parameters to estimate the investment mothers or others have to spend subsidizing children. Results suggest that maternal-juvenile cooperation can support the early transition toward a reduction in birth intervals, a longer period of juvenile dependence, and having overlapping young. The need for adult cooperation is most evident when birth intervals are short and age at net production is late. Findings suggest that the needs of juveniles would not have been an early selective force for adult cooperation. Rather, an age-graded division of labor and the mutual benefits of maternal-juvenile cooperation could be an important, but overlooked step in the evolution of cooperative breeding.     

Linkage Disequilibrium in Human Ribosomal Genes: Implications for Multigene Family Evolution

Members of the rDNA multigene family within a species do not evolve independently, rather, they evolve together in a concerted fashion. Between species, however, each multigene family does evolve independently indicating that mechanisms exist which will amplify and fix new mutations both within populations and within species. In order to evaluate the possible mechanisms by which mutation, amplification and fixation occur we have determined the level of linkage disequilibrium between two polymorphic sites in human ribosomal genes in five racial groups and among individuals within two of these groups. The marked linkage disequilibrium we observe within individuals suggests that sister chromatid exchanges are much more important than homologous or nonhomologous recombination events in the concerted evolution of the rDNA family and further that recent models of molecular drive may not apply to the evolution of the rDNA multigene family.     

Effects of Harsh and Unpredictable Environments in Adolescence on Development of Life History Strategies

The National Longitudinal Study of Adolescent Health data were used to test predictions from life history theory. We hypothesized that (1) in young adulthood an emerging life history strategy would exist as a common factor underlying many life history traits (e.g., health, relationship stability, economic success), (2) both environmental harshness and unpredictability would account for unique variance in expression of adolescent and young adult life history strategies, and (3) adolescent life history traits would predict young adult life history strategy. These predictions were supported. The current findings suggest that the environmental parameters of harshness and unpredictability have concurrent effects on life history development in adolescence, as well as longitudinal effects into young adulthood. In addition, life history traits appear to be stable across developmental time from adolescence into young adulthood.

Dynamic Acclimation of Photosynthesis Increases Plant Fitness in Changing Environments

Plants growing in different environments develop with different photosynthetic capacities—developmental acclimation of photosynthesis. It is also possible for fully developed leaves to change their photosynthetic capacity—dynamic acclimation. The importance of acclimation has not previously been demonstrated. Here, we show that developmental and dynamic acclimation are distinct processes. Furthermore, we demonstrate that dynamic acclimation plays an important role in increasing the fitness of plants in natural environments. Plants of Arabidopsis (Arabidopsis thaliana) were grown at low light and then transferred to high light for up to 9 d. This resulted in an increase in photosynthetic capacity of approximately 40%. A microarray analysis showed that transfer to high light resulted in a substantial but transient increase in expression of a gene, At1g61800, encoding a glucose-6-phosphate/phosphate translocator GPT2. Plants where this gene was disrupted were unable to undergo dynamic acclimation. They were, however, still able to acclimate developmentally. When grown under controlled conditions, fitness, measured as seed output and germination, was identical, regardless of GPT2 expression. Under naturally variable conditions, however, fitness was substantially reduced in plants lacking the ability to acclimate. Seed production was halved in gpt2− plants, relative to wild type, and germination of the seed produced substantially less. Dynamic acclimation of photosynthesis is thus shown to play a crucial and previously unrecognized role in determining the fitness of plants growing in changing environments.It has long been recognized that when plants are grown under a particular set of conditions they adjust their photosynthetic capacity to match those conditions (for review, see Walters, 2005). For example, early work from Bjorkman and Holmgren (1963) showed that plants of Solidago virgaurea had different photosynthetic capacities when grown either in sun or shade. In spite of its long history, however, neither the mechanism nor the significance of this response is understood (Walters, 2005). Work from Murchie and Horton (1997) showed that there is substantial variation between species in their ability to acclimate, with plants from semishaded habitats having the greatest variation in photosynthetic capacity, suggesting that there is both a benefit and cost of acclimation. Neither benefit nor cost has been demonstrated.Photosynthetic acclimation can be observed at levels ranging from whole-plant morphology to the detailed stoichiometry of the photosynthetic apparatus (Boardman, 1977; Walters, 2005). Plants grown at low light tend to invest more in leaves than in roots and to have thinner leaves. They have more chlorophyll-containing light-harvesting proteins relative to light-using enzymes involved in electron transport and metabolism, meaning that photosynthesis saturates with light at a lower irradiance. Plants can also adjust the relative proportions of the different photosystems to suit the light quality they experience (Chow et al., 1990; Walters and Horton, 1995a, 1995b).Most studies that have examined the acclimation of plants have done so by making measurements on material that has experienced only one set of conditions—e.g. either high or low light. Differences between plants therefore reflect the conditions experienced as the leaves develop, with leaf morphology and composition being optimized for the conditions seen. Plants do not, however, exist in static environments. Even for a plant growing in an unshaded location, the light incident on a leaf can vary by an order of magnitude from second to second, day to day, and week to week depending on the weather conditions. This variation will typically be accompanied by variation in the temperature, which will also impact on metabolic capacity.When plants are exposed to light at irradiances that are above saturating for photosynthesis, which may result from increases in light or from environmental conditions (e.g. cold, drought) restricting metabolism, they are liable to suffer from stress (Demmig-Adams and Adams, 1992). Specifically, excess light can give rise to reactive oxygen species (Asada, 2006). The damaging effects of this can be limited by investing in antioxidant systems; however, these are metabolically expensive with, for example, substantial amounts of individual antioxidants such as ascorbic acid, being found in the chloroplast (Asada, 2006). It seems likely therefore that the ability of a plant to minimize stress, by adjusting photosynthetic capacity to suit as well as possible the prevailing conditions, will benefit the plant and increase overall fitness.In this study, we have investigated photosynthetic acclimation of the model plant Arabidopsis (Arabidopsis thaliana). Starting with a microarray analysis, we have identified a gene that is essential for acclimation to increases in irradiance. We further show that the ability to acclimate to changes in light has a major role in determining fitness under naturally variable light conditions.     

Children's Help and the Pace of Reproduction: Cooperative Breeding in Humans

Because children's ability to support themselves falls below their consumption, human young are subsidized by others throughout much of their growth and development. Mothers, however, who often have multiple dependents of different ages, are faced with an allocation problem (Fig. 1). This has led to important debate about the evolution of a long period dependence and the development of nonmaternal strategies to provision young. This article focuses on the critical role that children themselves play. Because the human subsistence niche incorporates a broad diversity of resources that require variable procurement and processing costs, dependent children can also be important producers, furthering both a need and an opportunity for cooperative breeding.     

Simulating Free-Roaming Cat Population Management Options in Open Demographic Environments

Large populations of free-roaming cats (FRCs) generate ongoing concerns for welfare of both individual animals and populations, for human public health, for viability of native wildlife populations, and for local ecological damage. Managing FRC populations is a complex task, without universal agreement on best practices. Previous analyses that use simulation modeling tools to evaluate alternative management methods have focused on relative efficacy of removal (or trap-return, TR), typically involving euthanasia, and sterilization (or trap-neuter-return, TNR) in demographically isolated populations. We used a stochastic demographic simulation approach to evaluate removal, permanent sterilization, and two postulated methods of temporary contraception for FRC population management. Our models include demographic connectivity to neighboring untreated cat populations through natural dispersal in a metapopulation context across urban and rural landscapes, and also feature abandonment of owned animals. Within population type, a given implementation rate of the TR strategy results in the most rapid rate of population decline and (when populations are isolated) the highest probability of population elimination, followed in order of decreasing efficacy by equivalent rates of implementation of TNR and temporary contraception. Even low levels of demographic connectivity significantly reduce the effectiveness of any management intervention, and continued abandonment is similarly problematic. This is the first demographic simulation analysis to consider the use of temporary contraception and account for the realities of FRC dispersal and owned cat abandonment.     

SLiM: Simulating Evolution with Selection and Linkage

SLiM is an efficient forward population genetic simulation designed for studying the effects of linkage and selection on a chromosome-wide scale. The program can incorporate complex scenarios of demography and population substructure, various models for selection and dominance of new mutations, arbitrary gene structure, and user-defined recombination maps.     

揭秘鸟类合作繁殖的进化:以青藏高原特有物种地山雀作为模式系统的一项长期努力

鸟类合作繁殖系统的进化机制是行为生态学和进化生态学领域的热点,许多基本理论问题依然悬而未决.青藏高原草甸荒漠气候恶劣、植被贫乏,是地球上独特的生态地理区域.自2004年以来,我们以此极端环境的特有物种地山雀(Parus humilis)为模式系统,探讨合作繁殖系统的特征和适应方式.在掌握合作系统基本结构的基础上,将继续进行长期数据的积累.通过比较帮助者和独立繁殖者的终生适合度,检验亲属选择理论;建立时空尺度上合作繁殖与气候因子的关系,揭露生态压力的作用机制;理清不同种群合作繁殖与婚外父权的关系,阐明遗传单配制作为合作繁殖行为进化的驱动力;联系外源与内源因素,确定合作繁殖物种种群动态的调节机理.地山雀社会系统的神秘需要研究者用不懈的努力去探索.     

The Cooperative Breeding System of the Red-cockaded Woodpecker

The breeding system of the red-cockaded woodpecker is described based on data collected over six years from a population of 500 marked individuals in the Sandhills of North Carolina. Male-female pairs were the most common social unit (59%), but 30% of social units contained one or more adult helpers, and 11% consisted of solitary males. Helpers were almost exclusively male: 27% of males remained in their natal group as helpers for at least one year, whereas only four (1%) females did. Most breeding females remained as breeders in the same group from one year to the next (56%), but a surprising number (12%) moved to another group. Many movements were related to incest avoidance or mate death, but 39% involved deserting a mate, usually following successful reproduction. We suggest that females sometimes are forced from groups by immigrants or other group members. The median distance of movements by adult females was only 1.3 km. In contrast to females, no breeding males switched groups. Survival of both breeding (76%) and helper (80%) males was higher than that of breeding females (69%). Males exhibited two distinct life-history strategies. Some remained as helpers on their natal territory for one or more years, and became breeders by inheriting breeding status in the natal group (17% per year) or by replacing a deceased breeder in a nearby group (13% per year, median distance moved 1.0 km). Other males dispersed from their natal group permanently during their first year. Some of these males were floaters at age one year, others were solitary, and a few became helpers in a non-natal group, but many were breeders. In contrast to males that first functioned as helpers, those that dispersed after fledging moved long distances (median dispersal distance 4.5 km), longer even than dispersing female fledglings moved (median distance 3.2 km). The habitat saturation model of the evolution of cooperative breeding is based on selection between the two life-history strategies exhibited by male red-cockaded woodpeckers. The model therefore may be tested directly with this species. Another indication that this model is appropriate for this species is the existence of a resource (cavity trees) that might provide an ecological basis for habitat saturation.     

Cooperative Breeding in the Lake Tanganyika Cichlid Julidochromis ornatus

Cooperative breeding has been described for several cichlids from the genus Julidochromis (Perciformes: Cichlidae) under laboratory conditions, but field evidence is scarce. Here we describe the breeding system of the cichlid Julidochromis ornatus (Boulenger) in Lake Tanganyika (Zambia). Groups defended a breeding shelter under a large flat stone. Smaller group members stayed and fed under or close to the stone, actively guarded by the larger group members. Six out of 28 groups were newly established by breeders, joined by subordinates from a large pool of independent fish (comprising 50–70% of the total population), and four groups were seen to dissolve during a total of 77 observation days. Breeding groups consisted of a large breeding male and female with zero to five smaller subordinates (average 2). Larger breeders and subordinates were found in larger groups. All group members participated in territory defence and -maintenance, but the breeders were only present at the shelter 48% of the time, in contrast to the subordinates which guarded the breeding shelter 94% of the time. Smaller group members showed submissive behaviours to larger group members. We conclude subordinates in J. ornatus are helpers, but we did not find evidence that helpers increased the group’s current reproductive success. Personal observations combined with a literature review revealed at least 19 species of Lake Tanganyika cichlids show evidence of cooperative breeding, entirely confined to the substrate breeding tribe of the Lamprologini (24% of 80 species in total): 2 Chalinochromis spp., 5 Julidochromis spp., 12 Neolamprologus spp. More effort should be put into detecting cooperative breeding in American and Asian substrate breeding cichlid species.     

小檗科的花粉演化

以APG III定义的基部真双子叶分支（Basal Eudicots）中毛茛目（Ranunculales）小檗科（Berberidaceae）为研究对象,选取4个DNA片段（rbcL、matK、trnLF和26S rDNA）,利用最大似然法构建分子系统树,结合已报道的花粉形态数据,分析了该科16个属的花粉形态。选择花粉分散单位、极性、形状、大小、萌发孔数目、萌发孔位置、外萌发孔形状、覆盖层上元素、覆盖层纹饰和外壁厚度共10个关键性状,采用简约法推断了该科花粉的祖征、共衍征和演化式样。研究表明：单粒、等极、近球形、中等大小是小檗科花粉的祖征。无极、多萌发孔和周面孔是小檗亚科（Berberidoideae）的共衍征,支持其为一个单系。三萌发孔分别为鬼臼亚科（Podophylloideae）、南天竹亚科（Nandinoideae）各自的共衍征;覆盖层上元素不存在是小檗亚科和南天竹亚科的共衍征,将它们与鬼臼亚科区分开来,同时也支持了小檗亚科和南天竹亚科之间的姐妹关系。此外,对一些属花粉形态的演化意义进行了讨论,提出一些特殊的花粉性状可以用来定义某些属,如Bongardia和兰山草属（Ranzania）。     

Breeding Increases the Efficacy of Chondrostereum purpureum in the Sprout Control of Birch

We tested whether the pairing of selected isolates could be used to increase the efficiency of a decay fungus Chondrostereum purpureum (Pers. Ex Fr.) Pouzar to control hardwood sprouting in Finland. We paired C. purpureum strains efficient in sprout control or highly active in laccase production, and tested the efficacy of their progeny in spout control experiments. This procedure resulted in a strain with an efficacy superior to that of the parental strains. The mortality of birch (Betula pendula Roth. and B. pubescens Ehrh.) 1 cm in stump diameter was 78%, 56% and 9% for the best progeny, the best parental strain and the control, respectively. Mortality was only slightly higher for B. pendula than for B. pubescens but no significant differences were found between the number or maximum height of stump sprouts. Our results showed that cross breeding of this decay fungus is a good alternative in attempts to produce efficient biocontrol agents against hardwood sprouting.     

鸟类合作繁殖研究进展

合作繁殖是当前行为生态学研究的热点。目前,鸟类学工作者对鸟类合作繁殖开展了大量研究。本文在简单回顾鸟类合作繁殖研究历史发展基础之上,对鸟类合作繁殖的特征进行了归纳与总结,并依据最新研究对进化途径和进化假说进行了对比分析和探讨。最后,针对当前研究中存在的问题或不足,提出将来研究的目标和方向。     

Root Foraging Increases Performance of the Clonal Plant Potentilla reptans in Heterogeneous Nutrient Environments

Background

Plastic root-foraging responses have been widely recognized as an important strategy for plants to explore heterogeneously distributed resources. However, the benefits and costs of root foraging have received little attention.

Methodology/Principal Findings

In a greenhouse experiment, we grew pairs of connected ramets of 22 genotypes of the stoloniferous plant Potentilla reptans in paired pots, between which the contrast in nutrient availability was set as null, medium and high, but with the total nutrient amount kept the same. We calculated root-foraging intensity of each individual ramet pair as the difference in root mass between paired ramets divided by the total root mass. For each genotype, we then calculated root-foraging ability as the slope of the regression of root-foraging intensity against patch contrast. For all genotypes, root-foraging intensity increased with patch contrast and the total biomass and number of offspring ramets were lowest at high patch contrast. Among genotypes, root-foraging intensity was positively related to production of offspring ramets and biomass in the high patch-contrast treatment, which indicates an evolutionary benefit of root foraging in heterogeneous environments. However, we found no significant evidence that the ability of plastic foraging imposes costs under homogeneous conditions (i.e. when foraging is not needed).

Conclusions/Significance

Our results show that plants of P. reptans adjust their root-foraging intensity according to patch contrast. Moreover, the results show that the root foraging has an evolutionary advantage in heterogeneous environments, while costs of having the ability of plastic root foraging were absent or very small.     

The Evolution of Dimorphic Traits: Predicting the Genetic Correlation between Environments

Many traits vary in a dichotomous manner, although the underlying genetic determination is polygenic. The genetic basis of such dimorphic traits can be analyzed using the threshold model, in which it is assumed that there is a continuously distributed underlying character and the phenotype is determined by whether the character is above or below a threshold. Threshold traits frequently vary with environmental variables such as photoperiod, temperature and density. This effect can be accounted for using a threshold model in which (1) there is a critical value of the environmental variable at which a genotype switches to the alternate morph, and (2) switch (threshold) points are normally distributed in the population. I term this the environmental threshold (ET) model. I show that the ET model predicts that across environments differing in only one factor the genetic correlation will be 1. This prediction is supported by data from three wing dimorphic insects. Evidence is presented that the genetic correlation between environments differing in two components (temperature and photoperiod) is less than 1.