Pre-social benefits of extended parental care

The evolution of helping, in which some individuals forfeit their own reproduction and help others to reproduce, is a central problem in evolutionary biology. Recently proposed insurance-based mechanisms rely on a pre-existing life history with a long period of offspring dependency relative to the short life expectancies of adult carers: a lone mother's offspring are doomed if she dies young, whereas after a helper dies, other group members can finish rearing the offspring. A critical question, however, is how this life history could evolve in ancestral non-social populations, as offspring survival would then depend on a single, short-lived carer. Here, we resolve this paradox by focusing on the extended parental care inherent in prolonged dependency. We show experimentally that in non-social wasps, extended care can significantly reduce the impact of interspecific parasites. Under extended care, offspring are less vulnerable by the time they are exposed to parasites, and costs of parasitism are reduced because mothers have the option to terminate investment in failing offspring. By experimentally simulating aspects of extended care in a species where it is lacking, we demonstrate that neither benefit requires specialized behaviour. Such benefits could therefore offset the disadvantage of prolonged dependency in non-social species, thereby facilitating the evolution of helping.     

Future fitness and helping in social queues

Helpers in primitively eusocial and cooperatively breeding animal societies forfeit their own reproduction to rear the offspring of a queen or breeding pair, but may eventually attain breeding status themselves. Kin selection provides a widely accepted theoretical framework for understanding these societies, but differences in genetic relatedness do not explain a universal societal feature: the huge variation between individuals in helping effort. An alternative explanation for this variation lies in a fundamental trade-off faced by helpers: by working harder, they increase the indirect component of their fitness, but simultaneously decrease their own future survival and fecundity. Here, we show that individuals work less hard when they stand to lose more future fitness through working. We experimentally manipulated two components of future fitness in social queues of hover wasps (Stenogastrinae): a helper's chance of inheriting an egg-laying position, and the workforce available to rear her offspring should she inherit. After each manipulation, helpers increased or decreased their effort as appropriate to the change in expected future fitness that they experienced. Although helping provides significant indirect fitness benefits for hover wasps, our study shows that variation in the costs associated with helping is the major determinant of helping effort.     

Social parasitism by male-producing reproductive workers in a eusocial insect

The evolution of extreme cooperation, as found in eusocial insects (those with a worker caste), is potentially undermined by selfish reproduction among group members. In some eusocial Hymenoptera (ants, bees and wasps), workers can produce male offspring from unfertilized eggs. Kin selection theory predicts levels of worker reproduction as a function of the relatedness structure of the workers' natal colony and the colony-level costs of worker reproduction. However, the theory has been only partially successful in explaining levels of worker reproduction. Here we show that workers of a eusocial bumble bee (Bombus terrestris) enter unrelated, conspecific colonies in which they then produce adult male offspring, and that such socially parasitic workers reproduce earlier and are significantly more reproductive and aggressive than resident workers that reproduce within their own colonies. Explaining levels of worker reproduction, and hence the potential of worker selfishness to undermine the evolution of cooperation, will therefore require more than simply a consideration of the kin-selected interests of resident workers. It will also require knowledge of the full set of reproductive options available to workers, including intraspecific social parasitism.     

The optimal sex ratio in cooperatively breeding populations

In some cooperatively breeding species, elder siblings remain within their home ranges to assist their parents in raising their younger siblings by providing protection or food. Previous attempts to model the popu- lation sex ratios of such species have assumed that helping is cost-free and only involves benefits to parents, resulting in offspring sex ratio biases towards the helping sex. However, parents may also incur costs in maintaining helpers. We incorporated costs and benefits of helping to predict the sex ratio of offspring in a theoretical model. Our model showed that the evolutionary stable strategy （ESS） sex ratio strongly depends on three parameters： （1） the average number of helpers per female; （2） the benefits that a helper brings to its mother＇s offspring production （MOP）; and （3） the cost-benefit ratio of helping. When one sex of elder siblings provides help, the ESS sex ratio is biased towards the helping sex if MOP costs are less than the benefits, （i.e., the cost-benefit ratio 〈1）. However, the ESS sex ratio becomes biased towards the non-helping sex if MOP costs exceed the benefits （i.e., the cost-benefit ratio 〉1）. Additionally, our model shows that the ESS sex ratio becomes biased in favor of the more helpful sex when both male and female elder siblings provide help. These results explain why sex ratios may become biased towards the helping sex, as well as the non-helping sex, in some species.     

Escalation of a coevolutionary arms race through host rejection of brood parasitic young

Cuckoo nestlings that evict all other young from the nest soon after hatching impose a high reproductive cost on their hosts. In defence, hosts have coevolved strategies to prevent brood parasitism. Puzzlingly, they do not extend beyond the egg stage. Thus, hosts adept at recognizing foreign eggs remain vulnerable to exploitation by cuckoo nestlings. Here we show that the breach of host egg defences by cuckoos creates a new stage in the coevolutionary cycle. We found that defences used during the egg-laying period by host superb fairy-wrens (Malurus cyaneus) are easily evaded by the Horsfield's bronze-cuckoo (Chrysococcyx basalis), a specialist fairy-wren brood parasite. However, although hosts never deserted their own broods, they later abandoned 40% of nests containing a lone Horsfield's bronze-cuckoo nestling, and 100% of nests with a lone shining bronze-cuckoo nestling (Chrysococcyx lucidus), an occasional fairy-wren brood parasite. Our experiments demonstrate that host discrimination against evictor-cuckoo nestlings is possible, and suggest that it has selected for the evolution of nestling mimicry in bronze-cuckoos.     

Queen activation of lazy workers in colonies of the eusocial naked mole-rat.

Evolutionary conflicts of interest are expected to arise in genetically diverse social groups. In eusocial insect societies, a potential conflict exists between the queen and her workers over how active the workers should be, and evidence exists that queen aggression increases activity levels of her lazier workers. Here I provide evidence that queen aggression (shoving) in laboratory colonies of the eusocial mammal, the naked mole-rat (Heterocephalus glaber), is a convergently evolved manifestation of queen-worker conflict over worker activity. Queen-initiated shoves activate inherently lazy workers, which tend to be larger and/or less related to the queen than are infrequently shoved, industrious workers. In addition, queen removal selectively depresses the activity of workers that are larger and less related to her. Finally, queen shoving and worker inactivity are pronounced when colonies are satiated but not when colonies are hungry, indicating that the underlying 'work-conflict' is highly context-specific.     

A brood parasitic catfish of mouthbrooding cichlid fishes in Lake Tanganyika

Brood parasitism, where a brood of the parasitic species is fostered by the parents of another species, is well known among birds. In most cases, such offspring show a complete reliance upon their host parents for food, protection and warmth until their independence. In other vertebrate groups, however, such total dependence upon a host species is unknown. I report here the first example of true brood parasitic behaviour discovered among fishes. In Lake Tanganyika, an endemic mochokid catfish, Synodontis multipunctatus Boulenger, is a brood parasite of mouthbrooding fishes of the family Cichlidae. The eggs of the catfish are incubated in the mouths of any of several host species together with the host's eggs, but hatch earlier. Following absorption of their yolk sacs, the catfish fry feed upon the fry of the host while still in its mouth. Thus the early stages of development of this catfish not only depend upon their hosts for food and protection, but exploit almost their entire parental investment.     

Sexual swellings advertise female quality in wild baboons

The females of many Old World primate species produce prominent and conspicuous swellings of the perineal skin around the time of ovulation. These sexual swellings have been proposed to increase competition among males for females or to increase the likelihood of a female getting fertilized, by signalling either a female's general reproductive status, or the timing of her ovulation. Here we show that sexual swellings in wild baboons reliably advertise a female's reproductive value over her lifetime, in accordance with a theoretical model of honest signalling. Females with larger swellings attained sexual maturity earlier, produced both more offspring and more surviving offspring per year than females with smaller swellings, and had a higher overall proportion of their offspring survive. Male baboons use the size of the sexual swelling to determine their mating effort, fighting more aggressively to consort females with larger swellings, and spending more time grooming these females. Our results document an unusual case of a sexually selected ornament in females, and show how males, by mating selectively on the basis of the size of the sexual swelling, increase their probability of mating with females more likely to produce surviving offspring.     

Sexual conflict reduces offspring fitness in zebra finches

Parental care is often costly; hence, in sexually reproducing species where both male and female parents rear their offspring (biparental care), sexual conflict over parental investment can arise. Such conflict occurs because each care-giver would benefit from withholding parental investment for use with another partner, leading to a reduction in the amount of care given by one parent at the expense of the other. Here we report experiments to explore the prediction from theory that parents rearing offspring alone may provide greater parental investment than when rearing offspring together with a partner. We found that when the number of offspring per parent, and hence the potential workload, were kept constant, offspring received a greater per capita parental investment from single females than from both parents working together, and that males reared by single mothers were more sexually attractive as adults than their biparentally reared siblings. This difference between single- and two-parent families is due to a reduction in care provided by females when they care together with a male, rather than laziness by males or differences in the begging behaviour of chicks, supporting the claim that sexual conflict in biparental care can reduce the quality of offspring raised.     

Unrelated helpers in a social insect

High-resolution genetic markers have revolutionized our understanding of vertebrate mating systems, but have so far yielded few comparable surprises about kinship in social insects. Here we use microsatellite markers to reveal an unexpected and unique social system in what is probably the best-studied social wasp, Polistes dominulus. Social insect colonies are nearly always composed of close relatives; therefore, non-reproductive helping behaviour can be favoured by kin selection, because the helpers aid reproductives who share their genes. In P. dominulus, however, 35% of foundress nestmates are unrelated and gain no such advantage. The P. dominulus system is unlike all other cases of unrelated social insects, because one individual has nearly complete reproductive dominance over subordinates who could have chosen other reproductive options. The only significant advantage that subordinates obtain is a chance at later reproduction, particularly if the queen dies. Thus, P. dominulus societies are functionally unlike other social insects, but similar to certain vertebrate societies, in which the unrelated helpers gain through inheritance of a territory or a mate.     

True paternal care in a multi-male primate society

Although male parental care is rare among mammals, adult males of many cercopithecine primate species provide care for infants and juveniles. This care is often in the form of grooming, carrying, support in agonistic interactions, and protection against infanticide. For these behaviours to be interpreted as true parental care, males must selectively direct care towards their own offspring and this care must result in fitness benefits. With the exception of males defending probable offspring from infanticide, male primates living in multi-male, multi-female social groups have not been shown to selectively direct care towards their own offspring. We determined paternity for 75 juveniles in a population of wild savannah baboons (Papio cynocephalus) and collected data on interventions in agonistic disputes by adult males on behalf of juveniles as a form of male care. Here we show that adult males differentiate their offspring from unrelated juveniles and selectively support their offspring in agonistic disputes. As support in agonistic disputes is likely to contribute to rank acquisition and protect juveniles from injury and stress, this can be considered true parental care.     

Complex social behaviour derived from maternal reproductive traits

A fundamental goal of sociobiology is to explain how complex social behaviour evolves, especially in social insects, the exemplars of social living. Although still the subject of much controversy, recent theoretical explanations have focused on the evolutionary origins of worker behaviour (assistance from daughters that remain in the nest and help their mother to reproduce) through expression of maternal care behaviour towards siblings. A key prediction of this evolutionary model is that traits involved in maternal care have been co-opted through heterochronous expression of maternal genes to result in sib-care, the hallmark of highly evolved social life in insects. A coupling of maternal behaviour to reproductive status evolved in solitary insects, and was a ready substrate for the evolution of worker-containing societies. Here we show that division of foraging labour among worker honey bees (Apis mellifera) is linked to the reproductive status of facultatively sterile females. We thereby identify the evolutionary origin of a widely expressed social-insect behavioural syndrome, and provide a direct demonstration of how variation in maternal reproductive traits gives rise to complex social behaviour in non-reproductive helpers.     

Competition induces adaptive shifts in caste ratios of a polyembryonic wasp

An important transition in insect life-history evolution was the shift from a solitary existence to living in groups comprising specialized castes. Caste-forming species produce some individuals that reproduce and others with worker functions that have few or no offspring. Morphologically specialized castes are well known in eusocial species like ants and termites, but castes have also evolved in less-studied groups like thrips, aphids and polyembryonic wasps. Because selection acts at both the individual and the colony level, ratios of investment in different castes are predicted to vary with environmental factors like competition and resources. However, experimental evidence for adaptive shifts in caste ratios is limited owing to the experimental difficulty of manipulating factors thought to influence caste ratios, and because some species produce behaviourally flexible castes that switch tasks in response to colony needs. Unlike other caste-forming species, the broods of polyembryonic wasps develop clonally, so that increased production of one caste probably results in decreased production of the other. Here we show that the polyembryonic wasp Copidosoma floridanum alters caste ratios in response to interspecific competition. Our results reveal a distinct trade-off by C. floridanum between reproduction and defence, and show experimentally that caste ratios shift in an adaptive manner.     

香港恒生指数期权市场的过度反应现象研究

论文以香港恒生指数期权市场为实证,对期权隐含波动率的“期限结构”进行了建模和研究。实证分析表明期权的隐含波动率具有很强的“中心回复”特性,那么,在有效市场假设和Black-Scholes期权定价模型正确性的前提之下,当一个期限较短的期权的隐含波动率发生变动时,另一个其他方面与之完全相同,但期限较长的期权,其隐含波动率的变动幅度应小于前一个期权隐含波动率的变动幅度。然而,通过对香港恒生指数期权市场的实证分析,两种不同统计检验方法的结果都对香港恒生指数期权市场的有效性假设提出了质疑－－市场并不是有效的基于理性预期的,而是存在着显著的“过度反应”现象。     

Embryonic temperature determines adult sexuality in a reptile

Gonadal differentiation in amniote vertebrates is controlled by one of two mechanisms: genotypic sex determination (GSD) or environmental sex determination (ESD). After differentiation the fetal gonad produces sex steroid hormones which govern the development of other components of sexuality. Thus, the primary sex determiner is thought to operate solely as a trigger that initiates a cascade of events culminating in adult sex differences. In the leopard gecko (Eublepharis macularius), gonadal and morphological sex is determined by incubation temperature, with relatively 'hot' temperatures (32 degrees C) resulting in mostly male offspring and relatively 'cold' temperatures (26 degrees C) resulting in only female offspring. We report here that the reproductive behaviour and endocrine physiology of an adult is influenced by the temperature experienced as an embryo. Also, the perception of a female to courtship by a male is influenced by incubation temperature. These data indicate that incubation temperature, the primary determiner of sex in this species, has differential effects on adult sexuality.     

隆线溞及大型溞头胸甲及孵育囊上皮的构造

本文报道了两种枝角类的头胸甲及孵育囊上皮的构造。经文献检索,是首次报道。上皮呈多角形,上皮以突起的角相接,构成了很多孔隙,这些孔隙就是血淋巴腔。背缘及腹缘的血腔都很宽大。上皮细胞的外侧是角质膜,外角质膜很厚,有多层,内角质膜极薄,且有很多微孔。透射电镜观察到成体内侧上皮有微毛及褶突,有输送血淋巴内营养物质及排除废物的功能。外侧上皮未发现特殊的构造。上皮内具特殊的胞器,线粒体能分生小线粒体、分层的球状体,还有具鳞片的分泌细胞,它们都产自外侧上皮。血腔内发现一种有核的变形细胞。内外上皮细胞间有纵横肌纤维,它们的伸缩可能与血淋巴循环有关。     

鄂尔多斯盆地富黄地区延长组长6储层成岩作用

根据砂岩薄片、铸体薄片、扫描电镜、X衍射等研究表明,富黄探区延长组长6储层砂岩为低孔低渗储集岩,其岩石类型为长石砂岩和岩屑长石砂岩,磨圆以次棱—次圆为主,颗粒间以线性接触和点—线接触为主,孔隙式和孔隙—薄膜式胶结为主,砂岩具有成分成熟度低,结构成熟度高的特点.储集砂岩经历的主要成岩作用为压实作用、胶结作用、溶蚀作用和破裂作用.压实作用是导致孔隙度丧失的主要原因,造成的平均孔隙度丧失为30.89%,胶结作用造成的平均孔隙度丧失为6.98%,碳酸盐胶结物和次生加大是造成储层物性降低的主要胶结物.而溶解作用对砂岩平均孔隙度的增加为1.22%,是改善砂岩物性的重要途径.     

Developmental plasticity in the visual and auditory representations in the mammalian superior colliculus

Environmental factors play an important role in certain aspects of the development of sensory systems. But the way in which the maturation of different sensory modalities is coordinated is poorly understood. We have investigated this question neurophysiologically in the mammalian superior colliculus (SC), which contains topographically aligned maps of visual and auditory space. We report here that an essentially normal auditory map, in approximate register with the visual map, is found in the SC of adult ferrets reared with abnormal binaural localization cues. Also, if, early in life, one eye is deviated laterally, there is a compensatory shift in the auditory map, but early eye rotation totally disorders the auditory representation. These results imply that development of the auditory map is affected by visual activity or by information about eye position and that there is definite, but limited, capacity for the auditory map to reorganize so that it remains aligned with the visual map.     

黄颡鱼人工繁殖的初步研究

利用面积为2000m^2的鲫鱼池套养培育黄颡鱼亲鱼；采用不同的药物和剂量进行人工催产；利用家鱼孵化池进行流水孵化。实验结果表明：黄颡鱼在性成熟度基本一致的情况下，用LRH—A2 DOM PG(LRH—A2、DOM、PG分别为4ug、0．8mg、2．2mg)的配合药物来进行生产，催产率可达到95％。