Geographical variation in acoustic signals of the planthopper, Nilaparvata bakeri (Muir), in Asia: species recognition and sexual selection

Populations of the planthopper .Nilaparvata bakeri (Muir) were sampled from the Philippines (Luzon), Indonesia (Bali), India (Bihar) and Sri Lanka (Central Province) from the grass Leersia hexandra (Schwartz), and cultured in Cardiff. Low intensity vibratory signals produced by males and females during mate location and courtship were recorded and analysed. Obvious differences were found between male calling songs of insects from the Philippines and those from the other three areas. Smaller differences were detected between the Indonesian, Indian and Sri Lankan populations. Hybrids between Philippine and Indonesian, and Indonesian and Sri Lankan, insects were obtained freely in the laboratory. Male calls of F, hybrids were variable and intermediate between parentals. Mate choice experiments showed no significant assortative mating between the different populations. There was no indication of reproductive isolation and therefore of different biological species. The assumption that different male calling songs necessarily indicate the presence of different biological species is not confirmed in this example.     

Niche construction and the environmental term of the price equation: How natural selection changes when organisms alter their environments

Organisms construct their own environments and phenotypes through the adaptive processes of habitat choice, habitat construction, and phenotypic plasticity. We examine how these processes affect the dynamics of mean fitness change through the environmental change term of the Price Equation. This tends to be ignored in evolutionary theory, owing to the emphasis on the first term describing the effect of natural selection on mean fitness (the additive genetic variance for fitness of Fisher's Fundamental Theorem). Using population genetic models and the Price Equation, we show how adaptive niche constructing traits favorably alter the distribution of environments that organisms encounter and thereby increase population mean fitness. Because niche-constructing traits increase the frequency of higher-fitness environments, selection favors their evolution. Furthermore, their alteration of the actual or experienced environmental distribution creates selective feedback between niche constructing traits and other traits, especially those with genotype-by-environment interaction for fitness. By altering the distribution of experienced environments, niche constructing traits can increase the additive genetic variance for such traits. This effect accelerates the process of overall adaption to the niche-constructed environmental distribution and can contribute to the rapid refinement of alternative phenotypic adaptations to different environments. Our findings suggest that evolutionary biologists revisit and reevaluate the environmental term of the Price Equation: owing to adaptive niche construction, it contributes directly to positive change in mean fitness; its magnitude can be comparable to that of natural selection; and, when there is fitness G × E, it increases the additive genetic variance for fitness, the much-celebrated first term.     

Context-dependent effects of tail-ornament damage on mating success in black grouse

Male black grouse (Tetrao tetrix) may receive damage to theirtail ornaments, the lyre, during goshawk predation attemptsand during fights with other males. In this study we confirma previous observation that black grouse males with damagedtail ornaments suffer reduced mating success. In males thatheld territories on the edge of the leks, tail damage was unrelatedto mating success, whereas in central males damage was negativelycorrelated with mating success. We tested experimentally whetherabsence of damage is used by females in mate choice. In maleswith edge territories, intact, control males had higher matingsuccess than males with cut tails, but in males with centralterritories, lyre cutting had no effect on mating success. Theseresults suggest two interpretations. First, female choice alsodepends on factors other than tail damage such as position onthe lek and dominance. Second, the effect of tail damage iscontext dependent; in males that otherwise meet females standards(e.g., dominant males), the effect of tail damage is negligible,but in less dominant males, tail damage could be used by femalesin mate selection. The second interpretation provides an explanationfor why the data on unmanipulated and manipulated birds differ.In experimental central birds, factors other than tail damageprobably determine male mating success, whereas in experimentaledge birds such factors are probably absent and therefore taildamage is relatively more important. In central unmanipulatedbirds, however, males with natural damage are probably not chosenbecause tail damage and absence of other attractive traits arecorrelated. The absence of an effect on peripheral unmanipulatedbirds may be explained by their overall low mating success     

Female mate choice and male red coloration in a natural three-spined stickleback (Gasterosteus aculeatus) population

Under laboratory conditions, female three-spined sticklebacks(Gasterosteus aculeatus L.) show a mating preference for intenselyred-colored males. We verified this female choice in the fieldby observing a freshwater stickleback population in its naturalhabitat. During the egg collection phase, individual courtingmales were localized with the aid of a dummy of a ripe female,caught and photographed under standardized conditions, and released.After males had stopped collecting eggs, we counted the numberof eggs in the nests. The more intense a male's red breedingcoloration, the more eggs he received. Simultaneous female choiceexperiments in the laboratory suggested that ripe females ofthis population preferred redder males. Breeding activitiesof the males in the field were clustered and seem to be synchronizedwithin clusters. At one of the breeding sites, more intensered males were in better physical condition, but this was notthe case at another site. Although several synchronized breedingcycles were observed, the majority of males seem to completeonly one breeding cycle.     

Female mating behavior in the field cricket,Gryllus pennsylvanicus (Orthoptera: Gryllidae) at different operational sex ratios

The influence of operational sex ratio on the mating behavior of female field crickets,Gryllus pennsylvanicus, was investigated. Females were predicted to be more discriminating under conditions of high mate availability and show less selectivity when males were rare. Such selectivity was indicated in this study with the proportion of courtships leading to a mating changing with sex ratio. Females accepted almost 70% of all courtships at the female-biased sex ratio, but only about half of all courtships were successful at even or male-biased sex ratios. Females moved least at the female-biased sex ratio. There was also a trend for females to be guarded more under male-biased conditions. Female weight did not influence any of the behaviors examined.     

Female mate choice and mating costs in the polyandrous butterflyPieris napi (Lepidoptera: Pieridae)

Males of the green-veined white butterfly (Pieris napi L.) transfer large ejaculates that represent on average 15% of their body mass when mating for a first time. Shortly after mating a male is able to transfer only a small ejaculate when mating a second time. Male ejaculate production plays a crucial role in the mating system ofP. napi because females use male-derived nutrients for egg production and somatic maintenance. Here we study how timing of female rematings and copulation duration are influenced by the mating history of their mates and, also, study if females exert mate choice to minimize their mating costs. Mating with a recently mated male increased female mating costs by increasing time in copula and mating frequency. Virgin females that mated with virgin males remated after an average of 6 days, whereas virgin females that mated with recently mated males remated after an average of 2 days. Moreover, copulations involving recently mated males lasted on average almost 7 h, whereas copulations involving virgin males lasted on average 2 h. Recently mated males were eager to remate, in spite of the fact that the size of the ejaculate they transfer is small and that they remain in copula for a long time. Hence it seems that males are more successful in the sexual conflict over mating decisions and that females do not minimize mating costs by choosing to mate preferentially with virgin males.     

A new cryptic irritant and cocarcinogen from seeds of Croton sparciflorus

In recent years the genus Croton has been of particular interest following the isolation of 11 different 12,13-diesters of the polyfunctional diterpene phorbol (1a), from the seed oil of Croton tiglium; these compounds represent its toxic, irritant and cocarcinogenic principles [1]. In addition, croton oil contains what is called “cryptic” cocarcinogens of the phorbol-12,13,20-triester type [1]. The structurally related but non-irritant diterpene ester 20-acetoxy-9-hydroxy-13,15-seco-4α-tigliatriene-(1,6,14)-dione-(3,13) [2] and crotofolin A have been isolated from C. rhamnifolius [3] and from C. corylifolious L. [4], respectively.     

Adult movement of the native holly leafminer,Phytomyza ilicicola Loew (Diptera: Agromyzidae): consequences for host choice within and between habitats

Summary Phytomyza ilicicola is a specialist herbivore, the larvae of which mine, and the adults of which feed and oviposit on the developing leaves of American Holly, Ilex opaca. Adult Phytomyza have been shown to discriminate among host plants on the basis of several host and habitat factors. Such discrimination may explain, in part, the observed density variation of larval Phytomyza among individual trees and between forest and suburban habitats. In order for discrimination to influence density, adult Phytomyza must be sufficiently vagile to move among habitats and to encounter many hosts. We experimentally monitored the movement of adults to ask if this were so. In addition we asked whether inter-host movements were altered by resource concentration, and whether vagility offered an escape from parasitism. To answer these questions, three isolated holly trees to serve as colonization sources were selected in early spring, prior to adult emergence. Potted target trees were then placed singly and in groups of four at 3 compass directions around and at 3 different distances (10, 25, and 50 m) from each of the source trees. Six weeks after exposure to adult Phytomyza, the number of feeding punctures and first instar larvae were counted. Clones were then overwintered in cold frames and in early spring, just prior to adult emergence, all pupae were examined for parasitism by the dominant parasitoid Opius striatriventris. Feeding and parasitism were similar at all 3 distances from the source trees, indicating that Opius was at least as vagile as Phytomyza. However, first instar larvae decreased with distance. There was no evidence that resource concentration affected adult movement. Our results suggest that Phytomyza are sufficiently vagile to choose among hosts within and between habitats. However, movement does not translate into equally high oviposition at all distances from a source, nor does it provide an escape from parasitism by Opius.     

Male mating competition,female choice and dominance in a free ranging group of Japanese macaques

Focal and ad libitum samples of high and middle ranked males in a group of free ranging Japanese macques were taken in order to examine rank related differences in male mating strategies. Males tended to have like ranked females as consort partners, with high rank males showing more consort activity, over all, than middle rank males. High rank males tended to interfere in consorts and middle rank males tended to have their consorts disrupted. Consorts involving high rank females were most subject to interference. With one exception, proximity between partners in consorts involving high rank males was due to male actions while proximity in consorts involving middle ranked males was due to female actions. The two highest ranked males were never observed copulating. Their mating failure may have been due to avoidance by females who had known them since immaturity. High rank males were somewhat more likely than middle rank males to have consorted with females during the period of likely conception. There was some evidence that frequent consort partners joined the same subgroup during a group fission. Males appeared to use the advantage conferred by high rank mainly in competition for high rank females. Females showed some indications of preference for mates likely to retain or attain high rank in the future.     

The effect of male size on receptivity in femaleLucilia cuprina (Diptera: Calliphoridae)

The first five matings by both large and small L. cuprinamales switched off receptivity in over 90% of females for 7 days after their initial mating. Small males were virtually unable to switch off females after five matings, whereas the fifth to tenth matings by large males rendered nearly two-thirds of females unreceptive. Mating duration of large and small males was about 11 min even after numerous matings. Given the rarity of field virgins and the temporal and spatial variability of female-required resources, larger males may enjoy greater mating success due to their ability to switch off many females in succession. Virgin males preferred to mate with nonvirgin females larger than themselves; males paired with females smaller than themselves adopted mate-rejection behavior typical of unreceptive females.