Quantifying male attractiveness and mating behaviour through phenotypic size manipulation in the Trinidadian guppy, Poecilia reticulata

Although many studies have examined the effects of male size on attractiveness and mating behaviour, few have taken genetic background into consideration. Phenotypic manipulation permits the experimental adjustment of morphological traits while keeping genetic background constant. Here, male guppies, Poecilia reticulata, an ideal model for this type of manipulation, were raised at different temperatures to produce sibling pairs that differed in size. These were then used to investigate male mating behaviour and male attractiveness, assessed through female mate choice, in relation to this size dimorphism. Further, male–male competition, which is intrinsic to male mating behaviour, is also likely to be affected by their size. Through the use of repeated measures analyses we demonstrate that females significantly prefer larger males and male size and competition significantly affect several aspects of male mating behaviour. Larger siblings perform more sneaky mating attempts and spend more time chasing females. The frequencies of both these behaviours increase with competition. While display frequency is unaffected by male size and competition, display duration and the amount of time spent attending females are reduced in the presence of competitors. This study highlights the use of phenotypic manipulation as a valuable tool for investigating behavioural interactions and confirms that both male size and competition are significant factors in the guppy mating system.     

Interspecific competition in tree squirrels: do introduced grey squirrels (<Emphasis Type="Italic">Sciurus carolinensis</Emphasis>) deplete tree seeds hoarded by red squirrels (<Emphasis Type="Italic">S. vulgaris</Emphasis>)?

Red squirrels (Sciurus vulgaris) and introduced eastern grey squirrels (S. carolinensis) scatterhoard seeds of broadleaf trees. Scatterhoarded seeds are an essential resource in spring and their consumption increases red-squirrel fitness. We examined whether grey squirrels partly deplete the high-energy food resources cached by red squirrels, reducing their consumption, in two ways: (1) at the population level, comparing energy intake of feeding on cached seeds between a study site with red and grey squirrels and one with only red squirrels present; and (2) at the individual level, in the study site where species co-exist, relating hoard recovery of red squirrels to the amount of core-area overlap with grey squirrels. There were no significant site differences in the mean daily energy intake of red squirrels feeding on seeds recovered from caches. However, in the red-grey site, during spring, red squirrels that had a high percentage of their home-range core area overlapped by grey squirrels had a lower daily energy intake than low-overlap red squirrels. Body mass of red squirrels in spring was negatively correlated with the percentage of interspecific core-area overlap, but not with core-area overlap with other red squirrels. Our data suggest that interspecific competition for scatterhoarded seeds, with grey squirrels pilfering red squirrels' food caches, caused a reduced energy intake in red squirrels with a high degree of interspecific core-area overlap, and reduced body mass in spring. Therefore, cache pilfering is likely to reduce reproductive output in red squirrels, and thus play a role in the replacement of red by grey squirrels. Electronic Publication     

Evolution of male dimorphic allometry in a population of the Japanese horned beetle <Emphasis Type="Italic">Trypoxylus dichotomus septentrionalis</Emphasis>

I conducted a detailed morphological analysis of the Japanese horned beetle Trypoxylus dichotomus septentrionalis to clarify the allometric relationship between horn length and body size and examined its mating success and reproductive behaviour in the field. The relationship between horn and body size was not discontinuous at the switch point body size, but the slope of the linear relationship changed at the switch point. Shape of the allometric relationship was initially steep and became flatten around the switch point in both linear and log scales; that is, minor males showed a positive relationship and major males showed a negative one. Major males gained more mating success than minor males. Within major males, individuals with larger horn or body size had higher mating success than individuals with smaller ones. Within minor males there were no differences in horn and body size between mated and unmated individuals. Although sneak-like behaviours were exhibited by both morphs, it is likely that these behaviours rarely lead to direct benefit. These results suggest that dimorphic allometry of T. dichotomus is consistent with the hypothesis of a continuous reaction norm that meets a ceiling, which restrains further allometric growth.     

Fertilisation success in the fly Dryomyza anilis (Dryomyzidae): effects of male size and the mating situation

Male fertilisation success in relation to male size and the mating situation (ordinary pair formation with a single, nonvirgin female vs. take overs) was examined in the fly Dryomyza anilis. In ordinary matings, large males achieved higher fertilisation success than small ones when they were the second to mate with the female. Take overs differ from ordinary pair formation in that the second male experiences intensified sperm competition. This is because in take overs the female is not able to discharge any of the sperm inseminated by the first male as she usually does before a new mating. Compared with ordinary matings, take overs reduced the fertilisation success of the second male by 8–10%, whereas that of the first male was 7–14% higher in take overs. Even though the intruder was always larger than the paired male his superior fertilisation success did not compensate for the effect of the sperm already present in the female. In D. anilis, males can increase their fertilisation success by tapping the female's external genitalia with their claspers or having several copulation bouts per mating. Thus, in a take over, the intruder could respond to the intensified sperm competition by performing more tapping sequences per copulation bout or more copulation bouts per mating. In matings observed in the wild, males performed more tapping sequences after a take over than after pair formation with a single female, although the difference was not significant. The results show that there are differences in fertilisation success between males of different size. In addition, different mating situations can result in considerable variation in the fertilisation success of an individual male. Higher fertilisation success for the first male after a take over may be significant, in particular, for the reproductive success of small males, which frequently lose their females to large males.     

Chemical mimicry of cuticular hydrocarbons – how does Eremostibes opacus gain access to breeding burrows of its host Parastizopus armaticeps (Coleoptera, Tenebrionidae)?

Summary. Breeding burrows of Parastizopus armaticeps armaticeps, a fossorial desert tenebrionid beetle, are cleptoparasitised by the closely related Eremostibes opacus. Gas chromatographic analyses show a high congruity of the cuticular hydrocarbons of both species. We compare these hydrocarbon patterns with those of four other Stizopina species and the Scaurini Herpiscius sommeri. In a bioassay, dummies treated with cuticular hydrocarbon extracts of E. opacus and the P. a. bifidus parasite E. bushmanicus were mostly ignored by P. a. armaticeps, whereas dummies with applied extracts of the remaining species were heavily attacked. We show that there is a correlation between agonistic behaviour of P. a. armaticeps towards the intruder and the chemical similarity of the cuticular hydrocarbons of the two species. Furthermore, we produced quantitatively modified hydrocarbon patterns of E. barbatus by changing the temperature at which this species was kept. The new 30 °C type was chemically similar to E. opacus, and was frequently ignored by P. a. armaticeps, whereas a reduction of the temperature to 20 °C only had minor effects on the hydrocarbon pattern. Furthermore, we show that the addition of one single component, heptacosane, to the cuticular hydrocarbon extract of E. opacus alters the host’s reaction. We discuss the role of cuticular hydrocarbons for the recognition of this host-parasite system and the relevance of quantitative characters in the hydrocarbon pattern for the discrimination of the host.     

Host-plant leaf surface compounds influencing oviposition in Delia antiqua

Summary. Delia antiqua (Diptera: Anthomyiidae) females lay eggs between the leaves of onion plants or in the soil around the base of the plants, then the maggots feed on the onion bulb and roots causing rapid secondary infection by fungi and bacteria. It is well known that the first sensory modality used by the onion fly is vision, therefore the shape (vertical narrow cylinders) and colour (yellow) of the plant play a crucial role in the recognition of a potential host plant. In the past it has been shown that n-dipropyl disulfide (Pr₂S₂), a typical component of onion volatiles, is an important chemical host plant cue. We extracted host leaf surface to verify if Pr₂S₂ is the major chemical oviposition stimulant and to determine if other as yet unknown substances may play a role in host-plant selection. We confirmed that the females laid more eggs around onion plants with leaves than when only the onion bulb was present and that the odour of chopped onion stimulates oviposition. Extraction of the surface of onion leaves revealed that only the apolar fraction contained substances that stimulate egg-laying in D. antiqua. GC-EAD analysis indicated that a minor constituent, Pr₂S₂, is perceived by the olfactory receptor on the antennae of the onion fly females. This confirmed the importance of Pr₂S₂ as oviposition stimulant. Contact with the polar fraction did not stimulate egg-laying behaviour in this Delia species. We discuss the oviposition strategy of D. antiqua in comparison with its closely related species, D. radicum, in which the oviposition behaviour is stimulated mainly through contact with the cabbage leaf surface and only partially by the host volatiles.     

Differential timing of spring migration in northern wheatears Oenanthe oenanthe: hurried males or weak females?

In a field experiment on the island of Helgoland (southeast North Sea), we investigated whether migration strategy or competition between the sexes cause the differential timing of spring migration of male and female northern wheatears (Oenanthe oenanthe) (males migrating earlier). The study included two subspecies, heading towards Greenland/Iceland and Scandinavia, respectively, and is based on colour-ringing and remote weighing of individuals. Despite food offered ad libitum, most Scandinavian birds left the island on the day of arrival or stayed only 1–3 days, whereas more than half of Greenlandic/Icelandic birds stayed for up to 12 days and refuelled rapidly. In the latter subspecies, males showed a positive correlation of departure fuel load and fuel deposition rate, resembling time-minimizers in optimal migration theory. In contrast, females departed irrespective of fuel deposition rate, with an approximately constant level of fuel stores. This level was lower than in males, but sufficient to enable by-passing of stopover sites en route, allowing us to regard females as time-minimizers also. Since females are not able to reach Greenland without additional refuelling elsewhere and males appeared to have a larger potential for by-passing stopover sites, time-selection seems to be more pronounced in males and may be the reason for earlier migration of males. Intraspecific aggressive interactions between colour-ringed birds were predominantly won by the initiator, by males and by larger birds, whereas fuel load and subspecies did not affect the outcome. Although compared to females, males were more often dominant at the feeding stations or held territories, refuelling patterns could not be explained by dominance. Subordinate or non-territorial birds did not refuel at a lower rate or depart with lower fuel loads than dominant or territorial birds. In non-territorial birds, the restricted access to feeding stations was made up with larger doses of food taken per visit, leading to the same energy intake as that of dominant and territorial birds. Therefore, competition during stopover could be eliminated as the reason for differential timing of migration of male and female wheatears, but this result may be species-specific.Communicated by W. Wiltschko     

Pups crying bass: vocal adaptation for avoidance of age-dependent predation risk in ground squirrels?

In most mammals, larger adult body size correlates with lower fundamental frequency and more closely spaced formants in vocalizations relative to juveniles. In alarm whistles of two free-living rodents, the speckled ground squirrel Spermophilus suslicus and yellow ground squirrel S. fulvus, these cues to body size were absent despite prominent differences in body weight and skull and larynx sizes between juveniles and adults. No significant correlations were found between the individual maximum fundamental frequency and body weight, both within age classes and for pooled samples of all animals within species. Furthermore, the mean alarm whistle maximum fundamental frequencies did not differ significantly between age classes (juvenile versus adult) in the speckled squirrel and were even significantly lower in juvenile yellow squirrels. We discuss the hypothesis that the obfuscation of vocal differences between juvenile and adult squirrels may represent a special adaptation of pup vocal behaviour—a form of “vocal mimicry,” resulting in imitation of adult vocal pattern to avoid infanticide and age-dependent predation risk.     

人员可靠性与系统安全

论述了人员可靠性对系统安全的影响，分析了它的特点和应采用的研究方法，介绍了笔者近年来在核电站人员可靠性基础研究方面的情况，并对研究的发展趋势进行了展望。     

Emotions,habits and rational choices in ecological behaviours: The case of recycling and use of public transportation

Two field studies examined the role of attitudes, subjective norms, perceived control, anticipated emotions, past behaviour and desire in the prediction of pro-environmental behavioural intention. The model of goal-directed behaviour (MGB) was applied to predict intentions to use public transportation instead of the private car for going to work (Study 1, N=180), and to recycle household waste (Study 2, N=154). Multiple regression and structural equation modeling were used to test the hypotheses in studies 1 and 2, respectively. As expected, results of the two studies indicate that negative anticipated emotions and past behaviour are significant predictors of desire to engage in pro-environmental action. Desire, in turn, positively predicts pro-environmental behavioural intentions. A direct link between past behaviour and intentions was also detected. Implications of the results for the promotion of pro-environmental behaviour are discussed.