Sexual selection in a wolf spider: Male drumming activity, body size, and viability

Females are often believed to actively choose highly ornamented males (males with extravagant morphological signals or intense sexual display), and ornaments should be honest signals of male viability. However, this belief is relying only on some pieces of empirical evidence from birds. Our study reports active female choice on sexual display that indicates male viability in spiders. We established trials in which we studied female choice in relation to male courtship drumming activity and body size. Females chose the most actively drumming males as mating partners, but the body size of the males did not seem to be selected. Male drumming activity turned out to be a good predictor of male v…

Overwintering survival in relation to body mass in a field population of the wolf spider ( Hygrolycosa rubrofasciata )

Body size is often considered to be an important trait affecting individual fitness. In arthropods, females commonly benefit from larger size directly through increased fecundity (Roff, 1992), and males through increased mating success (Andersson, 1994). It has also been suggested that larger individuals may in general have a better survival than smaller individuals (Calder, 1983; Peters, 1983). From this suggestion it may be predicted that during stressful environmental conditions larger individuals should do better than smaller individuals.

Microhabitat selection and audible sexual signalling in the wolf spider Hygrolycosa rubrofasciata (Araneae, Lycosidae)

We studied the microhabitat selection and male sexual signalling behaviour in the wolf spider Hygrolycosa rubrofasciata (Ohlert). Males strike dry leaves with their abdomen, producing an audible sexual drumming signal, and females use this signal to choose mating partners. In the field we followed male drum- ming rate and microhabitat selection using both the mark-recapture method and direct observations. In the laboratory we conducted an experiment on male micro- habitat and drumming substrate selection. We found that in the field males were not distributed randomly among the habitat; fewer males were found in areas that had high sedge cover, low elevation, and low dry leaf cover. In the l…

Female choice for male drumming in the wolf spiderHygrolycosa rubrofasciata

Mate preferences in invertebrates have usually been studied with simultaneous choice exper- iments alone, which allows eVective detection of any preferences but does not tell much about the strength of inter-sexual selection. Under natural conditions females frequently have to rely on sequential choice, and choosy females may incur opportunity and direct costs such as loss of time when they reject a male. Female preference in the wolf spider Hygrolycosa rubrofasciata for two components of male courtship signalling, rate and volume, was investigated. Both of these characteristics were tested with a sequential choice set-up and the eVect of volume also with a simultaneous choice method. Femal…

Background Despite the two-fold cost of sex, most of the higher animals reproduce sexually. The advantage of sex has been suggested to be its ability, through recombination, to generate greater genetic diversity than asexuality, thus enhancing adaptation in a changing environment. We studied the genetic diversity and the population structure of three closely related species of bag worm moths: two strictly sexual (Dahlica charlottae and Siederia rupicolella) and one strictly asexual (D. fennicella). These species compete for the same resources and share the same parasitoids.

Restrictive mating by females on black grouse leks

In bird species with pair bonds, extra-pair matings could allow females to choose genetically superior males. This is not needed in lekking species because female choice is not constrained by pairing opportunities. However, polyandry has been reported in most lekking species studied so far. Using 12 microsatellite loci, we determined the paternity of 135 broods of black grouse sampled between 2001 and 2005 (970 hatchlings and 811 adult birds genotyped). The paternity assignments were combined to lek observations to investigate the mating behaviour of black grouse females. About 10% of the matings seemed to take place with males displaying solitarily. Forty per cent of the copulations betwee…

Sexual selection in the wolf spider Hygrolycosa rubrofasciata: female preference for drum duration and pulse rate

The unusual form of sexual signaling, the drumming produced by the wolf spider Hygrolycosa rubrofasciata, allows exceptionally detailed studies of female preference patterns against signal characteristics. It is easy to manipulate the signals and to use large numbers of females in playback experiments. Males of H. rubrofasciata produce drums by striking their abdomen against dry leaves on the ground. Drums travel not only as substrate-borne vibrations, but also as airborne acoustic signals. Females respond sooner to drums transferred as substrate borne, but the mode of signal transfer has no effect on female preference for different types of drums. We investigated the effects of two key com…

Acoustic signalling in a wolf spider: can signal characteristics predict male quality?

While there has been considerable interest in female choice for male sexual signals, there have been few studies of the underlying information that different aspects of the signal calls convey. Such studies, however, are essential to understand the significance of signals as honest handicaps, arbitrary Fisherian traits and/or in species recognition. We studied the somewhat exceptional system of audible drumming in the wolf spider Hygrolycosa rubrofasciata. We estimated the repeatabilities of signal components, the levels of between-male variance, the symmetry of the signal, the correlations between different aspects of drumming and their correlations with body weight. While in other taxa th…

Do female leaf beetles Galerucella nymphaeae choose their mates and does it matter?

The role of active female choice in sexual selection is frequently difficult to ascertain, and this is particularly the case for many insect species. Also, it is uncertain whether choosing between males would affect offspring viability. We designed an experiment to investigate the presence of female choice in a Coleoptera species (Galerucella nymphaeae). We also estimated whether mate choice would have any effect on offspring performance. Females were first placed with two males in a test arena to see which of the males copulated with the virgin female, and how quickly. Subsequently the loser male was offered a new virgin female to test for any change in latency time until mating. The two-m…

Energetic costs of size and sexual signalling in a wolf spider

A prerequisite for honest handicaps is that there are significant condition–dependent costs in the expression of sexual traits. In the wolf spider Hygrolycosa rubrofasciata (Ohlert), sexual signalling (drumming) is costly in terms of increased mortality. Here we investigated whether this mortality may be caused by increased energy expenditure. During sexual signalling, metabolic rate was 22 times higher than at rest and four times higher than when males were actively moving. Metabolic rate per unit mass was positively related to absolute body mass during sexual signalling but not during other activities. This positive relationship is novel to any studies of metabolic rates. Indeed, it seems…

Viability costs of condition-dependent sexual male display in a drumming wolf spider

According to the conditional handicap models females use male ornaments as honest signals of male viability. The assumptions for honest signalling are that the traits are costly and that they reflect male phenotypic condition, and hence optimal trait size is largest in the most viable males. However, experimental evidence for the costs of signalling are scarce. In this study we experimentally tested whether acoustic signalling, drumming, in a wolf spider Hygrolycosa rubrofasciata is a condition dependent, costly trait, and thus offers an honest signal of quality to females. Males of this species court females by drumming dry leaves with their abdomen. Females prefer to mate with males of hi…

Sexual signalling and viability in a wolf spider ( Hygrolycosa rubrofasciata ): measurements under laboratory and field conditions

This study examined the crucial prediction of the conditional-handicap theory, the relationship between male sexual trait size and male viability, in the wolf spider Hygrolycosa rubrofasciata. In this species, males court females by drumming dry leaves with their abdomen, and males with the highest drumming rate enjoy highest mating success. We determined male drumming rate, body mass, and mobility, which reflects mate-searching activity, in relation to male survival. Because it is often difficult to know how results obtained from laboratory studies reflect the natural world, particularly when the measured variable is survival, we repeated our study in both laboratory and field conditions. …

Male mating success and risk of predation in a wolf spider: a balance between sexual and natural selection?

1.  Traits that benefit males through sexual selection are simultaneously expected to impair males by provoking costs through natural selection. If we consider the two male fitness components, mating success and viability, then we may expect that the increase in male mating success resulting from a larger trait size will be counterbalanced by an increase in viability costs. 2.  We studied the benefits and costs of male mate searching and sexual signalling activity in the wolf spider Hygrolycosa rubrofasciata. In the field, males search females actively and court them by drumming dry leaves with their abdomen. Females have been shown to prefer males with high drumming rate. Male moving and e…

Adaptive significance of synchronous chorusing in an acoustically signalling wolf spider

Synchronous sexual signalling is a behavioural phenomenon that has received considerable theoretical interest, but surprisingly few empirical tests have been conducted. Here, we present a set of experiments designed to determine (i) whether the sexual signalling of the drumming wolf spider Hygrolycosa rubrofasciata is synchronous, and (ii) whether the synchrony may have evolved through female preference. Using controlled playback experiments, we found that males actively synchronized their drumming bouts with other males and females significantly preferred closely synchronized drumming clusters compared with loose clusters. In loose clusters, the first drumming signals attracted the most fe…

Honesty of agonistic signalling and effects of size and motivation asymmetry in contests

Game theoretical models predict that the main function of fighting behaviour is to assess the relative fighting ability of opponents. The sequential assessment game has often been used to investigate contests, while honest signalling theory has received much less attention. With the wolf spider Hygrolycosa rubrofasciata we investigated whether male agonistic signalling can reveal honest information about fighting ability, and how size and motivation asymmetries affect male fighting behaviour. We also determined whether male–male competition affects the courtship behaviour of the males. We found that agonistic drumming activity is an honest indicator of male fighting ability, and that relati…

Mate choice for offspring performance: major benefits or minor costs?

There is considerable disagreement over whether or not gaining viability benefits to offspring could be substantial enough to overcome the costs of female choosiness. A recent review suggested that the 'lek paradox' might be resolved by large indirect benefits as indicated by highly heritable ornamental traits. We selected males of a wolf spider Hygrolycosa rubrofasciata in relation to their sexual signalling rate (audible drumming). The estimated correlated response in offspring viability was rather small (0.12 s.d.). However, it may be large enough if the costs of being choosy are small. In fact, females mate with better-than-average males just by responding passively to a random drumming…