Male reproductive polymorphism and form-specific habitat utilization of the damselflyMnais pruinosa (Zygoptera: Calopterygidae)

Habitat utilization patterns were studied in damselfly males,Mnais pruinosa, which have two male forms with different reproductive behaviors. The ‘esakii’ (orange-winged males) were territorial around oviposition sites, while the ‘strigata’ (hyaline-winged males) were non-territorial, often sneaking into theesakii's territory or loitering on the foliage of vegetation along stream banks. The place in the stream in the study area where females frequently appeared was covered by reeds and had abundant oviposition sites. It was difficult for the territorialesakii to stay there because the crowded reeds prevented them from defending their territory and discovering the females. Furthermore, there was competition for the limited territorial space with another species,Mnais nawai. Strigata males concentrated in this place in direct proportion to the number of females. Females frequently mated withstrigata males and probably deposited eggs fertilized bystrigata sperm rather thanesakii sperm. The density ofstrigata was higher than that ofesakii in this study area. If the average reproductive success ofesakii andstrigata males is equal, this may indicate that the equilibrious point between the two male forms is biased towardstrigata.     

松褐天牛的交配行为

采用室内试验和野外观察相结合的方法,对松材线虫病的主要媒介昆虫松褐天牛Monochamus alternatus Hope的交配行为进行了研究。结果表明： 松褐天牛一次完整的交配包括相遇抱对、插入输精和配后保护3个阶段,在交配过程中雄虫有多次插入输精现象发生。室内试验中共观察到松褐天牛的交配123次,松褐天牛一次完整的交配过程平均需时63.49 min,其中输精前的抱对时间平均为1.68 min,交配过程中每次输精插入时间平均为57.60 s,配后保护时间为15.18 min。松褐天牛在开始交配的4天内平均交配5.15次,不同雄性个体所获得的交配机会差异很大。松褐天牛的交配行为表现出强烈的雄性竞争现象,雄虫能根据雌虫或自身的交配经历调整交配投入,当雌虫或者雄虫是初次交配时,总输精时间和插入输精的次数显著大于与有交配经历的雌虫或雄虫交配时的输精时间和插入输精次数。田间松褐天牛的交配行为与室内观察结果基本一致。     

Overlapping territories ofPseudosimochromis curvifrons males and other herbivorous cichlid fishes in Lake Tanganyika

Males of the herbivorous cichlid fishPseudosimochromis curvifrons established mating territories 3–10 m in diameter, which included both spawning and feeding sites. Territorial males attacked conspecific males and also other species. Only conspecific males were chased out of the territories. Territorial males attacked other species at the spawning sites while courting or waiting for females and at other sites in their territories while patrolling and foraging. Attacks against herbivorous species were more frequent than against non-herbivores since herbivores were much more abundant. Territories of four abundant herbivorous cichlids largely overlapped the territories ofP. curvifrons males. Symbiotic relationships were not detected between the species. Instead, they were aggressive towards each other but coexisted by segregating feeding sites in the overlapping areas. The aggressive coexistence ofP. curvifrons males with other herbivores may have resulted from the energetic costs of defending their relatively large territories against all food competitors. Interspecific food-resource partitioning may also have facilitated the coexistence.     

Body size influences mating success of the Eucalyptus longhorned borer (Coleoptera: Cerambycidae)

Both sexes of adultPhoracantha semipunctata F. (Coleoptera: Cerambycidae) congregate on stressedEucalyptus that are the larval hosts. In a field study, 721 adultP. semipunctata captured on host trees varied considerably in body size with the largest individuals being about twice the length of the smallest. Females that were paired with a mate were similar in size to solitary females, suggesting that the probability of a female being mated was not affected by her size. However, large males had greater success than smaller males in obtaining mates. MaleP. semipunctata rely on antennal contact to locate and identify females on the larval host. Therefore, the rate at which males search for mates is a function of the area swept by their antennae per unit time. Because of their greater antennal spread, large males were able to search for females at double the rate of the smallest males. Large males also dominated in aggressive contests for females. The superior abilities of large maleP. semipunctata in both locating and defending mates account for the influence of body size on mating success.     

The male's dilemma: Increased offspring production is more paternity to steal

Summary Large potential effects of male care on the number of offspring females successfully raise are not sufficient to select for caring males because of the pervasive importance of mating competition. Males face a version of the social dilemma, in which increased production increases the pay-off for theft. Models of the allocation of male effort partitioned between caring for babies and competing for paternity show that the optimal allocation to care is very low under a wide range of conditions. Like sex allocation where the alternatives are male versus female function or sons versus daughters, the pay-offs to one alternative are always strongly frequency dependent. Because that alternative (male function, sons, male mating effort) pays so well when rare, it cannot remain rare under most conditions. Here we consider the consequences of partitioning mating effort into mate guarding and all other forms of mating conflict. If a male gets all his partner's conceptions while guarding, gaining them at a constant rate, there are two possible regions of stability. The evolutionarily stable strategy (ESS) depends on a parameter scaling the decisiveness of (non-guarding) mating conflict. When marginal returns from conflict decrease with scale, almost all effort goes into guarding. When marginal returns increase, the ESS devotes all effort to mating. Even when the potential effect of care is large, male equilibrium strategies allocate little effort to it. We also report the results of computer simulations showing that care increases if gains from guarding saturate quickly, so that a male is assured of the paternity of most of his partner's offspring with little guarding, and consequently the pool of unguarded conceptions open to competion shrinks sharply. But even when the male's dilemma is very much reduced, it still substantially limits the allocation to care. The results of both computer simulations and mathematical analysis converge with other lines of evidence that mating has much stronger effects than parenting in shaping male strategies.     

Male Reproductive Success in a Promiscuous Armoured Catfish Corydoras Aeneus (Callichthyidae)

Among a variety of fish mating systems, promiscuity with random-mating seems to be most prevalent. However, detailed studies of promiscuity have been rare due partly to the peculiar difficulty in examination of male mating and reproductive success in the random mating. Females of the armoured catfish Corydoras aeneus (no sexual dimorphism other than size of males > females) spawn 10–20 egg-clutches with multiple males at a time, but an entire egg clutch is inseminated by sperm of a single male. We studied mating system of this fish in aquarium. Males had neither mating territories nor monopolized females, never being aggressive against rival males. Evidence of female preference for certain male traits including size was not detected. Females mated a male in proportion to his relative courtship frequency among males. Courtship frequency was not related to male size, and male mating success was not different between small and large males. Clutch size and insemination rate were different neither between small and large males nor between frequently and less frequently courting males. Thus, the male reproductive success will not be related to the male size, but directly to courtship frequency, indicating the random mating in this fish. There seemed to be fecundity advantage with size in female, and the consequent sexual difference in energy allocation will be responsible to the sexual dimorphism. We also discuss the low male-GSI in this promiscuous fish in which sperm competition hardly occurred.     

温度和种间竞争对大型溞种群动态和两性生殖的影响

在20℃、25℃下,将大型溞和老年低额溞分别按7+3(B组),5+5(C组),3+7(D组)的组合进行混合培养,以及用单种培养(10+0(A组),0+10(E组))作为对照,研究了温度和种间竞争对大型溞种群动态和两性生殖的影响.实验结果表明:在混合培养时,大型溞对老年低额溞产生明显的竞争优势.20℃、25℃下,单种培养的老年低额溞最大种群密度分别为大型溞的2.31和1.97,而在混合培养下老年低额溞的种群密度明显低于大型溞,在实验25d后几乎全部死亡.25℃下两种溞的种群密度之间存在极显著的负相关性(C组:r=-0.508,n=30,P<0.01;D组:r=-0.483,n=30,P<0.01).在20℃、单种培养下,大型溞在首次产幼溞时即出现雄体,且种群密度与雄体密度呈显著的相关性(r=0.678,n=24,P<0.01).大型溞的最大雄体密度(106 ind.(200ml)~(-1))和最大雄体比例(36.8%)均出现在20℃、单种培养下.25℃下,大型溞在混合培养的B组和C组首次产幼溞时即出现雄体,且雄体在混合培养B组的比例达28.2%.大型溞在25℃、单种培养下没有产生卵鞍,在混合培养下总计产生66个卵鞍,其中空卵鞍占51.5%,而在20℃、混合培养下没有卵鞍产生.实验结果暗示:在较高的温度下,种间竞争刺激了大型溞雄体的产生和卵鞍的形成,高密度的雄体有助于大型溞孤雌生殖雌体向两性生殖雌体的转化.     

长苞铁杉天然林群落种内及种间竞争关系研究

通过各种竞争指数的比较筛选,得到较能客观反映长苞铁杉种内、种间竞争关系的竞争指数,定量地分析了长苞铁杉种内和种间竞争强度。结果表明:长苞铁杉种内竞争随胸径的增大而逐渐减少;种间与种内竞争关系顺序为:长苞铁杉-长苞铁杉>猴头杜鹃-长苞铁杉>青冈栎-长苞铁杉>其它树种-长苞铁杉。竞争强度与对象木的胸高直径服从双曲线回归关系,利用模型预测了长苞铁杉种内、种间的竞争强度。     

Interspecific mating in the Piriqueta caroliniana (Turneraceae) complex: effects of pollen load size and composition

Two taxa of Piriqueta (P. caroliniana and P. viridis) form a broad hybrid zone that extends over much of the central Florida peninsula. We used genetic markers to examine the strength of the isolation barriers between these taxa and the patterns of mating at the initial stages of hybridization. Regression models were employed to analyze the effects of pollen load size and the proportions of intra- and interspecific pollen on the frequency of first-generation (F1) hybrid formation. Overall, the postpollination mating barriers between these two taxa were relatively weak. However, there were significant effects of pollen load composition and size on the patterns of hybridization in both taxa with frequency-dependent responses to composition in both taxa. The frequency of F1 hybrid formation was generally lower than expected based on the frequency of each pollen type on the stigma for P. caroliniana recipients. The lower frequencies of F1 seeds in this taxon were apparently due to a greater competitive ability for intraspecific pollen, since hybrid seed formation decreased with increasing pollen load size. Pollen from P. caroliniana donors was also competitively superior on P. viridis recipients, leading to higher than expected frequencies of hybrid seed formation. Pollen from P. caroliniana did suffer higher rates of pollen-tube attrition than intraspecific pollen on P. viridis recipients, so the frequency of hybrid seed formation would be lower when pellen load sizes were small. In general, reproductive isolation mechanisms were stronger in P. caroliniana, suggesting that introgression should occur into P. viridis when these taxa come into close contact. Comparison of these expected patterns of mating to the distribution of hybrid genotypes in Florida provides insights into the relative roles of mating and selection in the evolution of hybrid populations of Piriqueta.     

Space use by the Japanese fluvial sculpin, Cottus pollux, related to spatio-temporal limitations in nest resources

Space use by the Japanese fluvial sculpin, Cottus pollux, as related to nest availability was studied in a Japanese mountain stream. Males had larger home ranges than females before breeding. A measure of nest resource limitation was L < 1 and the same nest rock was used by two males successively in three cases, indicating a limited supply of suitable nest rocks for males. All males included the nest rocks in their home ranges, but the timing of nest occupation was apparently dependent on male size, suggesting the presence of male-male competition for the nest rocks. Females, on the other hand, exhibited two different patterns in space use, independent of body size: (1) they spawned in their home ranges, or (2) they spawned out of their home ranges and returned. Nest cavity area did not affect male reproductive success. Spatial separation between female home ranges and nest location was the main reason for the females' movement out of their home ranges. The limitation in the male mating phase (5.7 days on average) might also have forced the females to move out of their home range to spawn. The reason behind such temporal limitation in the male mating interval was discussed from the viewpoint of the energy cost accompanying male parental care.     

昆虫在多次交配与精子竞争格局中的雌雄对策

绝大多数昆虫雌性一生中不但与不同雄性交配许多次,而且在其特殊器官中还可长期贮藏雄性精子,因此来自不同雄性的的精子在与雌性卵子受精时发生激烈的精子竞争。本文综述了昆虫在多次交配与精子竞争格局中的雌雄对策。雄性对策表现在对自身与配偶身体质量状况的正确评估、精子竞争风险预测、精子异型及延长交配时程和配后保护等,雌性对策则表现在对雄性质量状况的正确评估、对精液的主动操纵及精子偏向性等,从而很好地适因多次交配和精子竞争而带来的强烈自然选择和性选择压力。     

中国蜜环菌生物种新记录

在华中、西北和西南地区,发现了6个新的中国蜜环菌生物种CBS J、CBS K、CBS L、CBS M、CBS N和CBS O,研究证明都是异宗配合种类。CBS J与CBS A、CBS K与CBS G 以及CBS L与CBS H之间存在较低的互交可育现象。CBS K与Armillaria mellea互交可育, CBS M与A.borealis互交可育,且首次在欧洲以外地区被发现,其余4种为亚洲特有种。     

Ovulation mode modifies paternity monopolization in mammals

There are two forms of ovulation: spontaneous and induced. As copulation triggers ovulation for induced ovulators, males can predict the timing of ovulation and may have greater paternity monopolization than spontaneous ovulators. However, this prediction has never, to my knowledge, been tested. Using a cross-species comparison I examined the percentage of offspring sired within a litter (single paternity) and in social species the percentage of offspring sired by the dominant male (alpha paternity). My results indicate that ovulation mode alters the ability of males to monopolize paternity, with males of induced ovulators having higher single paternity and greater alpha paternity where male–female association is intermittent.