Responses of juvenile terrestrial salamanders to introduced (Lithobius forficatus) and native centipedes (Scolopocryptops sexspinosus)

When introduced species invade ecosystems, alterations in community structure can emerge from the competitive and predatory interactions that occur between introduced and native guild members. Because a number of recent studies have shown that large predatory invertebrates can both compete with and prey on small vertebrates and because introductions of non-native species may play a role in amphibian declines, the effects of introduced centipedes Lithobius forficatus and native centipedes Scolopocryptops sexspinosus on juveniles of the red-backed salamander Plethodon cinereus were examined. In laboratory arenas, juvenile salamanders exhibited submissive behaviour in response to the odours of both species of centipede. There were no significant differences in salamander response to the two centipede odour treatments, but compared to controls, juveniles of P. cinereus spent significantly more time in escape and in a flattened submissive posture when presented with native centipede odours. Despite significant size differences between centipedes and juvenile salamanders, no predation of salamanders by either species of centipede occurred in any pairings. Juveniles exhibited more chemosensory behaviour towards native centipedes and towards their odours and exhibited marked reductions in aggressive posturing when centipedes were present. Field and laboratory data suggest that juveniles of P. cinereus and centipedes were negatively associated. In laboratory trials, the native centipede excluded juvenile salamanders from cover objects and we found fewer instances of co-occurrence in the field than expected. These studies are the first to examine the behavioural interactions between juveniles of P. cinereus and invertebrate predators, one introduced and one native, of eastern deciduous forest-floor food webs.     

Inter-male aggression with regard to polygynous mating system in Pampean grassland mouse, Akodon azarae (Cricetidae: Sigmodontinae)

Based on the hypothesis that, in Akodon azarae, polygyny operates through female defence, we studied inter-male aggression in order to test the following predictions: during the breeding period (1) resident males are more aggressive than intruder males in the presence of females (FP), and (2) aggressive behaviour is independent of male condition (resident or intruder) in the absence of females (FA). To test our predictions, we used the resident male behavioural response towards an intruder male in relation to FP or FA. We conducted 30 encounters in FP and 27 in FA in 0.79-m² round enclosures placed in the Espinal Reservation. Our results support the prediction that, in FP, the intensity of aggressive behaviour exhibited by males varied in relation to resident or intruder condition. Resident males showed high levels of aggression towards intruders, and intruders exhibited the greatest values of submissive behaviours with residents. In FA, the intensity of aggressive behaviour did not vary in relation to resident or intruder condition. Both resident and intruder males exhibited low aggressive behaviour and inter-male encounters resulted mainly in non interactive behaviours. Our results support the hypothesis that, in A. azarae, the polygynous mating system operates through female defence.     

Are simple plumage traits sufficient for species discrimination by harrier males?

I investigated whether plumage features are sufficient for species recognition in two sibling sympatric raptor species: the Montagu's harrier Circus pygargus and the hen harrier C. cyaneus . These species are similar in body size and differ slightly in plumage. During prelaying and laying periods, I placed artificial models close to nests of both species, simulating a conspecific male harrier (male of the same species), a heterospecific male harrier (male of the other species) or a wood pigeon Columba palumbus (acting as a control of the same size and colour). All of them represented birds perched in a neutral posture, so that they could only be recognised by their plumage differences. The use of plumage traits during this period would be particularly relevant in discriminating between their own and other species, offering the opportunity to avoid unnecessary fights, and therefore maximising the benefits of defence. I measured male responsiveness by recording aggressive behaviour towards each model (aggressive rate and time spent close to the female). Male presence time was significantly longer during conspecific decoy presentation than during heterospecific decoy presentation. Furthermore, males of both species were more aggressive towards the conspecific decoy than towards the heterospecific one, and no attacks towards the control were recorded. These results provide evidence that these birds are able to recognise plumage features of their own and the sibling species.     

Mating behaviour of the water mite Arrenurus manubriator (Acari: Arrenuridae)

Water mites of the genus Arrenurus vary in male sexual dimorphism and in sperm transfer behaviour. Although it is a very large genus (≈800 spp.), mating behaviour has been described for only a few species. Here sperm transfer behaviour is described for the first time in a North American species, Arrenurus manubriator. Behaviour patterns can be divided into pre-pairing (readiness posture and cauda presentation), pre-deposition (high vertical jerking, low vertical shaking, striking/stroking and slow lateral waving), spermatophore deposition, sperm translocation, post-deposition (striking/stroking. slow lateral waving, 'tick-rock', shuttling, violent shaking), and separation. Males deposited 8–21 spermatophores in a mating. Pairs remained together for up to 31/2h. Possible adaptive functions of male courtship behaviour are discussed, including the hypothesis that male intromittant organs evolved in Arrenurus to circumvent female choice.     

The courtship and mating of the Iberian midwife toad Alytes cisternasii (Amphibia: Anura: Discoglossidae)

Sexual encounters were staged in the laboratory among hormonally-primed Iberian midwife toads, Alytes cisternasii . In this species, pairing and fertilization are terrestrial. The male cares for the developing embryos on land, carrying them twined around his hind limbs until they hatch into tadpoles which he releases into water; his investment in the offspring then ends. The courtship of A. cisternasii can be divided into a pre- and post-ovulatory phase. An encounter is initiated when the female approaches the male and is clasped by him in inguinal amplexus. Both the male and the female produce vocalizations during the period prior to the initiation of amplexus. During amplexus, only the female vocalizes, changing her call to one that is of lower intensity, longer duration and more regularly emitted than before. During inguinal amplexus, the male engages in bouts of intense pedalling and gentle rocking behaviour, each bout being initiated when the female repositions herself beneath him. Rocking and pedalling cease when the female ovulates, at which time she exhibits a posture that we call Unkenkrampf. Ovulation occurs at this time, and is followed by sperm release by the male (seen as a series of lateral compressions of his body). After sperm release, the male moves forwards to engage the female in cervical amplexus and then manoeuvres his hind limbs such that the egg string becomes tangled around his ankles. The female may exhibit additional episodes of Unkenkrampf during this period, but these are not accompanied by further egg release. Episodes of Unkenkrampf (without ovulation) also may occur after the male dismounts from the female. Similar behaviour patterns to those observed in the laboratory are seen in natural populations of A. cisternasii . We compare and contrast our observations of A. cisternasii with those of other authors for this species and also for the common midwife toad, A. obstericans .     

Assessing the potential for egg chemoattractants to mediate sexual selection in a broadcast spawning marine invertebrate

In numerous species, egg chemoattractants play a critical role in guiding sperm towards unfertilized eggs (sperm chemotaxis). Until now, the known functions of sperm chemotaxis include increasing the effective target size of eggs, thereby promoting sperm-egg encounters, and facilitating species recognition. Here, we report that in the broadcast spawning mussel, Mytilus galloprovincialis, egg chemoattractants may play an unforeseen role in sexual selection by enabling sperm to effectively 'choose' between the eggs of different conspecific females. In an initial experiment, we confirmed that sperm chemotaxis occurs in M. galloprovincialis by showing that sperm are attracted towards unfertilized eggs when given the choice of eggs or no eggs in a dichotomous chamber. We then conducted two cross-classified mating experiments, each comprising the same individual males and females crossed in identical male × female combinations, but under experimental conditions that offered sperm 'no-choice' (each fertilization trial took place in a Petri dish and involved a single male and female) or a 'choice' of a female's eggs (sperm were placed in the centre of a dichotomous choice chamber and allowed to choose eggs from different females). We show that male-by-female interactions characterized fertilization rates in both experiments, and that there was remarkable consistency between patterns of sperm migration in the egg-choice experiment and fertilization rates in the no-choice experiment. Thus, sperm appear to exploit chemical cues to preferentially swim towards eggs with which they are most compatible during direct sperm-to-egg encounters. These results reveal that sperm differentially select eggs on the basis of chemical cues, thus exposing the potential for egg chemoattractants to mediate mate choice for genetically compatible partners. Given the prevalence of sperm chemotaxis across diverse taxa, our findings may have broad implications for sexual selection in other mating systems.     

Multiple Cues in Status Signalling: The Role of Wingbars in Aggressive Interactions of Male House Sparrows

During aggressive interactions, animals may signal their competitive ability by various ornaments referred to as badges of status. The use of a single badge predicting dominance rank occurs in many vertebrate species. However, animals often display multiple ornaments that may convey information about either different or the same aspects of the signaller's quality, or alternatively, may serve as signal amplifiers. We observed the fighting behaviour of male house sparrows in two captive flocks to investigate whether they may use multiple cues in status signalling during aggressive interactions. Beside the status‐signalling bib, male sparrows possess a conspicuous white wingbar that they often display upon aggressive encounters. We tested whether bib size and the wingbar's conspicuousness (i.e. its achromatic contrast with the neighbouring dark feathers) or its area predicted success in various aspects of fighting. We found that bib size strongly predicted overall fighting success (i.e. proportion of fights won) and defence success (i.e. proportion of successful defences out of all attacks received). Wingbar conspicuousness was positively related to defence success after controlling for the effect of bib size in multivariate analyses. Furthermore, displaying the wings also tended to improve the birds’ success in defence but not in attack. Wingbar area was unrelated to any measured aspect of fighting ability. We suggest that bib size and wingbar conspicuousness may convey multiple messages on fighting abilities, specifically on overall aggressiveness and defending potential, respectively. Alternatively, wingbars may serve as amplifiers for the wing displays of aggressive motivation. Thus, male sparrows may use multiple cues in assessing the competitive ability of opponents during social interactions.     

Mating with sperm-depleted males does not increase female mating frequency in the parasitoid Lariophagus distinguendus

Sexual conflicts due to divergent male and female interests in reproduction are common in parasitic Hymenoptera. The majority of parasitoid females are monandrous, whereas males are able to mate repeatedly. Thus, accepting only a single mate might be costly when females mate with a sperm‐depleted male, which may not transfer a sufficient amount of sperm. In the present study, we investigated the reproductive performance in the parasitoid Lariophagus distinguendus Först. (Hymenoptera: Pteromalidae) and studied whether mating with experimentally sperm‐depleted males increases the tendency of females to remate. Males were able to mate with up to 17 females offered in rapid succession within a 10‐h test period. The resulting female offspring, as an indirect measure of sperm transfer, remained constant during the first six matings and then decreased successively with increasing number of copulations by the males. Experimentally sperm‐depleted males continued to mate even if they transferred only small amounts or no sperm at all. Unlike males, the majority of females mated only once during a 192‐h test period. A second copulation was observed only in a few cases (maximum 16%). The frequency of remating was not influenced by the mating status of the first male the females had copulated with, suggesting that these events are not controlled by sperm deficiency of the females. Furthermore, we investigated male courtship behaviour towards mated females. Male courtship intensity towards mated females decreased with increasing time. However, females that had mated with an experimentally sperm‐depleted male did not elicit stronger or longer‐lasting behavioural responses in courting males than those that had mated with a virgin male. As the observed behaviours in L. distinguendus are known to be elicited by a courtship pheromone, these results suggest that females no longer invest in pheromone biosynthesis after mating (as indicated by ceasing behavioural responses of courting males), irrespective of whether they have received a sufficient amount of sperm or not. We discuss the results with respect to a possible mating strategy of sperm‐depleted males.     

The Relationship Between the Presence of Satellite Males and Nest-Holders' Mating Success in the Azorean Rock-Pool Blenny Parablennius sanguinolentus parvicornis

In the Azorean rock-pool blenny, sexually active males may adopt alternative reproductive tactics. In the present paper the relationship between the presence of satellite males and the reproductive success of nest-holders was investigated by comparing nests with and without an associated satellite male. Males with an associated satellite male suffered more conspecific intrusions but they did not display a higher frequency of attacks towards conspecifics. Nest-holder males were more aggressive towards other conspecifics than towards satellites and the tolerance of nest-holders towards satellites was inversely correlated with the time spent by the satellites in the breeding territory, which suggests control by the nest-holder male of the satellite investment in shared territorial defence. Nest-holders with an associated satellite male had higher condition factors and received more female visits and more spawnings. These results bear two possible interpretations. (1) Nest-holders benefit from the presence of a satellite male by increased attractiveness of their nests to females; satellite males are mutualists helping to defend the nest-owner's territory and to attract females, which is why they are tolerated. (2) Satellite males associate preferentially with more successful nest-holder males which have higher condition factors, and by doing so have more opportunities to achieve parasitic fertilizations. Only experiments will allow these two hypotheses to be distinguished.     

Sex, Rank and Age Differences in the Japanese Macaque (Macaca fuscata yakui) Participation in Inter-Group Encounters

In many species interactions among group are often characterized by agonistic behaviour. Although animals may participate in inter‐group encounters in different ways, depending on their energetic requirements, reproductive tactics, and/or developmental stage, the proximate causes affecting an animal's participation in inter‐group encounters are still poorly understood. Indeed, many studies have analysed the behaviour of males and females during inter‐group encounters without considering the importance of additional factors (e.g. rank). This study focuses on wild non‐provisioned Japanese macaques (Macaca fuscata yakui) living on Yakushima Island, Japan. It aims to determine how monkeys of different sex, age, and rank behave during inter‐group encounters and it discusses the implications and consequences of their behaviour on group composition and male dispersal. Males participated significantly more than females in inter‐group encounters, by displaying more aggressive or affiliative behaviour. High‐ranking and/or adult males were more aggressive than low‐ranking and/or subadult males during encounters occurring in the mating season and they also showed more herding behaviour. This trend was not found in inter‐group encounters occurring during the non‐mating season. Finally, males which then emigrated to new groups were low‐ranking and/or subadult individuals. Those males displayed more affiliative behaviour towards foreign males than males which did emigrate. These data indicate that in non‐territorial species with male dominance over female and high competition for mating partners males play an active, and often aggressive, role during inter‐group encounter while female participation is scarce. Factors such as age, rank and period of the year (in seasonally breeding species) have to be taken into considerations when analysing interactions between groups and their effects on group composition and social behaviour.     

Remote copulation: male adaptation to female cannibalism

Sexual cannibalism by females and associated male behaviours may be driven by sexual conflict. One such male behaviour is the eunuch phenomenon in spiders, caused by total genital emasculation, which is a seemingly maladaptive behaviour. Here, we provide the first empirical testing of an adaptive hypothesis to explain this behaviour, the remote copulation, in a highly sexually cannibalistic orb-web spider Nephilengys malabarensis. We demonstrate that sperm transfer continues from the severed male organ into female genitals after the male has been detached from copula. Remote copulation increases the total amount of sperm transferred, and thus probably enhances paternity. We conclude that the mechanism may have evolved in response to sexual cannibalism and female-controlled short copulation duration.     

Mating duration and sperm precedence in the spider <Emphasis Type="Italic">Linyphia triangularis</Emphasis>

In many animal species, mating behaviour is highly ritualised, which may allow us to relate some of its consequences, e.g. male paternity and female receptivity, to the progression of phases in the mating sequence; at the same time, ritualisation raises the question of to what extent the partners, especially the males, are able to influence the outcome of mating for their own benefit. We studied the linyphiid spider Linyphia triangularis in which mating follows a strict sequence during which the male inducts two droplets of sperm and transfers them to the female. We performed sperm competition experiments (sterile-male technique) including four treatments, in which the copulation of the first male was interrupted at prescribed phases of the mating sequence, while the second male was allowed a complete mating. Second males spent a shorter time than first males on the behaviours prior to sperm transfer, but the amount of sperm (2 droplets) and the time spent in sperm transfer were independent of the females’ mating status. The proportion of females accepting the second male depended on the mating duration of the first male, i.e. whether the first male had transferred one or two sperm droplets. After a complete first mating, most females accepted no further males. A last-male sperm precedence was apparent if only half of the first sperm droplet had been transferred by the first male, but this switched to a first male precedence if one full sperm droplet had been transferred. Thus, even in the face of sperm competition, it is sufficient for the first male to transfer one sperm droplet. The second sperm droplet and the extended copulatory courtship associated with its transfer may serve to induce a lack of receptivity in the female, but the males seem unable to enhance their reproductive success through variable copulatory tactics.     

The role of female competition in the mating success of two clones of the Amazon molly, Poecilia formosa

Clones of the unisexual fish Poecilia formosa , the Amazon molly, live in the wild in association with their progenitor bisexual species, and compete with them for resources. These resources include food, space and also mates, since the Amazon molly reproduces gynogenetically, a process in which sperm transferred from a male host species activates their eggs. Earlier studies of the adaptive mechanisms that facilitate the coexistence of the bisexual and unisexual forms have focused upon male behaviour, but recent work with another unisexual species, Poeciliopsis , demonstrated that female aggressive behaviour may play an important part in determining the ecological standing of a clone.
We have extended our observations to female mating behaviour in two clones in the Amazon molly; clone 1 that does not thrive well under laboratory culture; and clone 2 that is hardy and survives very well. There was no aggression between the clones, nor did the clones show aggression towards females of the bisexual species. However, clone 1 consistently was more successful in the number of mating encounters made with the male; it approached the male more often than clone 2 and fled from the male less often. Males also showed some preference for mating with clone 1 females. If there are physiological differences in the wild clones similar to those seen in the laboratory, the mating advantage of the less robust clone 1 may ensure its continued survival in competition with a more vigorous clone.     

Mate choice in a hermaphrodite: you won't score with a spermatophore

Sexual selection has played a major role in shaping the wide variety of mating patterns found in species with separate sexes, but little is known about its effects on simultaneous hermaphrodites. However, many hermaphrodites possess complex reproductive systems and mating behaviour is often elaborate, suggesting that some form of mate assessment takes place. We found that the marine slug Aeolidiella glauca, a simultaneous hermaphrodite with reciprocal external sperm transfer via spermatophores, shows a unique mate choice behaviour by avoiding mating with conspecifics already carrying a spermatophore received during the previous mating. Current mating status did not seem to affect this behaviour, because both slugs that had mated 2-3 days before our mate choice trials and slugs that had been isolated for 4-6 weeks avoided spermatophore-carrying partners. There are two obvious reasons why slugs should avoid recently mated partners. First, they may reduce the risk of getting a partner depleted in self-sperm. Second, the risk of sperm competition may be decreased. Histological investigations of sperm reserves suggest that sperm depletion did not influence our mate choice experiments. Most slugs had sufficient sperm stored for spermatophore production. Therefore, the most likely explanation for A. glauca's peculiar mate choice is that, by avoiding a recently mated partner, a sperm donor may reduce its risk of being subjected to sperm competition.     

Chemosensory assessment of sperm competition levels and the evolution of internal spermatophore guarding

Males of many species adjust their reproductive behaviour according to the perceived risk of sperm competition. Although this phenomenon is widespread in insects and other animals, the mechanisms that allow mates to assess sperm competition levels remain largely unexplored. In this study, we analysed the mating behaviour of pairs of Tenebrio molitor beetles under three odour treatments representing increasing levels of sperm competition risk (SCR) and sperm competition intensity (SCI). Copula duration and male and female post-copulatory behaviour varied significantly with odour treatment. Both copula duration and post-copulatory associations (PCAs) increased significantly in odour treatments reflecting high male density. To our knowledge, this is the first study to report that insects may assess the actual density of potential competitors at the time of mating, a cue to SCR and SCI, on the basis of chemical cues. In T. molitor, males inhibit sperm release from the spermatophore of a rival male when remating takes place at short intervals. We show that, when sperm competition levels are high, PCAs increase female remating interval just above that necessary to prevent spermatophore inhibition by rival males. This finding strongly suggests that strategic male behaviour plays a 'spermatophore guarding' role in this species. Although common in insects with external spermatophore transfer, spermatophore guarding is not expected in species with rapid ejaculate transfer and internal spermatophore delivery. Our results reveal that spermatophore guarding may evolve, even under these circumstances, as an evolutionary response to short-term spermatophore inhibition or displacement mechanisms.     

Rival male relatedness does not affect ejaculate allocation as predicted by sperm competition theory

When females are sexually promiscuous, the intensity of sperm competition for males depends on how many partners females mate with. To maximize fitness, males should adjust their copulatory investment in relation to this intensity. However, fitness costs associated with sperm competition may not only depend on how many males a female has mated with, but also how related rival males are. According to theoretical predictions, males should adjust their copulatory investment in response to the relatedness of their male rival, and transfer more sperm to females that have first mated with a non-sibling male than females that have mated to a related male. Here, for the first time, we empirically test this theory using the Australian field cricket Teleogryllus oceanicus. We expose male crickets to sperm competition from either a full sibling or non-sibling male, by using both the presence of a rival male and the rival male's actual competing ejaculate as cues. Contrary to predictions, we find that males do not adjust ejaculates in response to the relatedness of their male rival. Instead, males with both full-sibling and non-sibling rivals allocate sperm of similar quality to females. This lack of kin biased behaviour is independent of any potentially confounding effect of strong competition between close relatives; kin biased behaviour was absent irrespective of whether males were raised in full sibling or mixed relatedness groups.     

Brood defence and parental roles in a biparental cichlid fishLamprologus toae in Lake Tanganyika

Brood defence of a cichlid fish,Lamprologus toae, was investigated in its natural habitat in Lake Tanganyika. Both parents guarding a brood attacked both conspecific and heterospecific intruder fishes at different locations. The heterospecific intruder fishes could be classified into three groups on the basis of the locations at which the attacks against each species took place. The distinction of groups by the parents seemed to be primarily based on food habits and feeding behaviour of the intruder fishes. The piscivorous species which were more dangerous for the brood were attacked by both parents at more distant locations from the brood. Parental defence of breeding territory changed with the development of the young. The frequency of attacks against each group decreased after the young reached the size too large for the fishes of the group to prey on. Division of labour in the territorial defence was recognized between male and female. The male parent mainly defended the peripheral region of the territory and the female parent defended the inner region. Significance of the selective attack against intruders and the division of labour between the two sexes in brood defence is discussed.     

Aspects of the mating behaviour of male mollies (Poecilia spp.)

The unisexual fish Poecilia formosa (the Amazon molly) reproduces by gynogenesis, a process in which sperm from the males of the host bisexual species activates development of its eggs. Unisexuals live with one of the host species in nature and compete with bisexual females for the males. It was long thought that male discrimination and mate selection established a balance between the unisexual and bisexual populations. Thus, hierarchies of males were set up in which dominant males mated with their conspecific females and subordinates mated with the Amazon molly. Recent evidence suggested, however, that male fish do not discriminate between their own females and the Amazon molly, and that there always are more males available than sexually receptive females of both species.
Our findings indicate that male behaviour may be more complex than suggested by either hypothesis. Mate discrimination and courtship behaviour appear to increase with age, so that large males show almost complete preference for their conspecific females, but smaller males will mate with the Amazon molly. In complex groups, small males often dart in and mate with their own females whilst the large males are engaged in courtship activities and defence of territory.     

Functions of duetting in the tropical boubou, Laniarius aethiopicus: territorial defence and mutual mate guarding

Duetting, found in many animal taxa, is still a poorly understood form of signalling behaviour despite numerous hypotheses to explain its function. One contentious issue is whether duetting is a cooperative endeavour or signals conflict between the sexes. We studied the function of duetting in the tropical boubou, using interactive playback experiments. We staged encounters by presenting paired birds with four variants of each of four duet types (neighbour and stranger solos and neighbour and stranger duets). Multiple lines of evidence suggest that both joint territorial defence and mutual mate guarding are important functions of duetting, and that both cooperation and conflict between males and females have shaped duetting behaviour. Of a repertoire of 12 duet types, eight were used for joint territorial defence. Two of these eight duet types were probably also used for mutual mate guarding, suggesting that individual duets can have multiple functions. We found an unusual response for duetting birds in that females often synchronized notes with male solo playback to form precise duets. In turn, males attempted to jam the song of rivals when females joined the song of male solo playback, providing further evidence for the importance of acoustic mate guarding. Song jamming by males has not previously been described for duetting species. Finally, we suggest that the repertoire of duet types is used to fine-tune territorial encounters in a network environment of multiple interactants.