Non-guarding Males Research Articles

Reason for being single: some males do not guard receptive females in the hermit crab Pagurus filholi

In animals that reproduce sexually, males are often under strong selection to maximize the number of mating opportunities. However, in some iteroparous species, males do not always maximize the allocation of time and energy to the present mating opportunity. Male hermit crabs of the genus Pagurus show precopulatory guarding as a mate acquisition strategy. Although almost all males within this genus guard and compete for receptive females, males of Pagurus filholi differ in how likely they are to do so. To examine the factors explaining the absence of guarding behaviour in P. filholi, a laboratory experiment was conducted that focused on whether either of two receptive females was guarded by solitary males that had been found not paired in the field, had lost a previous male–male contest or had copulated with other females. Solitary males showed a significantly lower frequency of guarding than males with experience of losing or of copulation. In the solitary group, males that moulted within 5 days after the experimental trial did not guard females, and the moulting frequency of nonguarding males was significantly higher than that of guarding males. In further analysis, smaller solitary males were shown to be less likely to guard females. The results of the experiment suggest that males of P. filholi may not always invest as much as possible in the present mating opportunity but may temporarily invest in growth during the 8-month mating season.

Mating system and exclusive postzygotic paternal care in a Neotropical harvestman (Arachnida: Opiliones)

This study tests predictions of the hypothesis of evolution of paternal care via sexual selection by using the Neotropical harvestman Pseudopucrolia sp. as the model organism. Females use natural cavities in roadside banks as nesting sites, which are defended by males against other males. Females leave the nests after oviposition, and all postzygotic parental care is accomplished by males, which protect the eggs and nymphs from predators. We provided artificial mud nests to individuals in the laboratory and conducted observations on the reproduction of the species. Male reproductive success was directly related to nest ownership time: the longer a male held a nest, the higher his chances of obtaining copulations. All males that succeeded in mating and obtaining one clutch eventually mated with additional females that added eggs to the clutch. Thus, desirable males were not limited to monogamy by paternal care. Experimental manipulations demonstrated that guarding males were more attractive to females than were nonguarding males and also that males guarded unrelated eggs. Finally, we found that females and nonguarding males spent more time foraging than guarding males. We use our data to contrast hypotheses on the origin and maintenance of paternal care and to provide a critical assessment of the hypothesis of the evolution of paternal care via sexual selection.

Changes in male physiological condition during brooding activities in a natural population of a stream goby, Rhinogobius sp.

We investigated the change in physical condition of males during paternal care in a natural population of a stream goby Rhinogobius sp. LD. Hepatosomatic index (HSI) and Condition factor (K) of males guarding an egg mass were higher than those of non-breeding males. In the first brooding cycle, the HSI of males decreased with the progress of embryo development. Moreover, in the second brooding cycle, both the HSI and K decreased, suggesting that the energy reserves in the somatic tissue were used when the liver reserves were exhausted as a source of energy for paternal activities. After paternal care, males showed reduced K and were unable to recover HSI immediately. Comparisons of the physical condition between non-guarding males after the first brooding cycle and males guarding an early stage clutch in the second brooding cycle indicated that males which could recover HSI and K were able to have a second brooding cycle. This suggested that the physical condition determines participation in breeding activity and the number of brooding cycles, greatly influencing male reproductive success.

Life‐history variation in relation to nest site abundance in males of the freshwater goby Tridentiger brevispinis

Abstract – Age at maturity in males of the freshwater goby Tridentiger brevispinis, a species with exclusive paternal care, was investigated in two populations in Lake Biwa, Japan, that differed markedly in nest site abundance. At Ohmi‐maiko, where nest sites were scarce, most males matured at age 3, and mean body size of males guarding eggs in nests was larger than that of males sampled randomly (including both guarding and nonguarding males) in the population. Conversely, at Minamihama, where nest sites were abundant, many males matured at age 1, and there was no difference in body size between guarding males and males collected randomly. The slope of regression lines between body size of the guarding male and the number of eggs in his nest was greater in Ohmi‐maiko than in Minamihama. These results suggest that the shortage of nest sites enhances reproductive success in larger males, probably through male–male competition for nest sites and female mate choice for larger males. I conclude that in nest spawners, the availability of nest sites should strongly affect life‐history traits of males through sexual selection.

Foraging time of rutting bighorn rams varies with individual behavior, not mating tactic

Mate guarding is the primary mating tactic used by dominant males of many species of ungulates. Guarding males are thought to forage less during the rut than do nonguarding males, possibly leading to greater fitness costs. I observed bighorn rams foraging during the pre-rut and the rut. I compared how coursing (an alternative mating tactic) and tending (a form of mate guarding) affected the foraging behavior of bighorn rams over the rut, to test whether foraging was more constrained by mate guarding than by coursing. All adult males spent less time feeding during the rut compared with the pre-rut. The decrease in time spent feeding, however, was independent of mating tactic. Contrary to expectation, individual rams observed both coursing and tending spent less time foraging when coursing than when tending. For young rams, the time spent in rutting activities was correlated with individual pre-rut mass, indicating that males either modify their behavior according to available metabolic reserves or adjust the energy devoted to rutting activities to the level of expected benefits. Mate guarding does not appear to constrain foraging more than coursing. The costs of male reproductive behavior may depend more upon individual effort than on the particular tactic adopted. Copyright 2005.

Quantification of sexual dimorphism in Asellus aquaticus (Crustacea: Isopoda) using outline approaches

A marked sexual dimorphism is often observed in arthropods species in which males perform precopulatory mate guarding. It is generally thought to reflect the influence of sexual selection. Until now, sexual dimorphisms associated with mate guarding have mainly been qualitatively described. However, assessing the effects of sexual selection on sexual dimorphims requires a preliminary quantitative assessment of differences in morphology between sexes. Using Fourier analyses, we tested if morphological dimorphisms could be quantitatively assessed in the isopod Asellus aquaticus. In addition, we checked whether sexual dimorphism in shape was exclusively related to mate guarding through considering characters that are not, a priori, implicated in mating behaviour. To assess the potential role of sexual selection in shaping morphology, we then examined how dimorphic characters could influence males' pairing success. Three characters (pleotelson, paraeopods 4 and 5) differed significantly in shape between males and females. In addition, two characters (pleotelson and paraeopods 4) differed in shape between guarding males and non-guarding males, with the latter being closer in shape to females. This suggests that sexual selection may be partly responsible for the observed morphological divergence between sexes in A. aquaticus.

Parental investment of male two-spotted goby, Gobiusculus flavescens (Fabricius).

The trade-off between parental care and feeding was studied in the male two-spotted goby (Gobiusculus flavescens F.). Two temperatures, 8.5 degrees C and 13.0 degrees C, were used, with five replicates at each temperature, in order to determine whether temperature influenced parental behaviour. In each replicate, two males and four females were introduced to an aquarium, where the males chose between two nests and courted the females. In each replicate, one male spawned. After spawning, the males guarded the eggs until hatching. The guarding males' behaviour was recorded with a video camera twice a day (15 min each time), once before and once after they were fed. The male's condition (c-factor) was calculated at the start of the experiment and after egg hatching. The eggs were spawned in an artificial nest (half of a PVC tube), and attached to the nest in a single layer. The areas with eggs (representing brood size) were marked after spawning and the fry counted after hatching (which was used to calculate area hatched). Numbers of prey eaten (plankton) and number of aggressive encounters between the guarding male and the other fishes were recorded. Time spent in the nest and time used on fertilisation, fanning and cleaning were estimated and related to egg age, brood size, hatching success, temperature and food availability (no food or food).The results showed that feeding (expected to influence future reproduction) decreased and parental expenditure (current reproduction) increased, as the eggs developed (became closer to independence). Parental expenditure was significantly higher at 13.0 degrees C than at 8.5 degrees C, presumably due to higher oxygen demands by the eggs, and a greater risk of egg-infections. The c-factor of the males guarding eggs decreased over time, in contrast to the non-guarding males' c-factor. Guarding males' aggressiveness decreased as the eggs got older, but increased just before hatching. A possible explanation for this could be the decreasing intrusion by the non-guarding male and females caused by high aggressive behaviour by the guarding male early in the brood cycle. The exploitation of the nest (percentage of total nest area covered by eggs) seemed to determine the amount of parental expenditure and loss of condition, while brood size (area of eggs) had no effect.

Trade-offs between postcopulatory riding and mate location in the blue milkweed beetle

In the blue milkweed beetle, Chrysochus cobaltinus (Coleoptera: Chrysomelidae), males remain stationary on females' backs for prolonged periods after a single, brief copulation. Lone males often attack pairs, and takeovers, in which rival males replace the resident on the female's back, are common. I used removal experiments to measure the effect of postcopulatory riding on latency to remating. Females whose males were removed were more likely to remate in the next 2 h than females that were allowed to remain paired. When females were removed, males were also more likely to remate in the 2-h period following removal than were males allowed to continue riding. This indicates that males delay remating by their mates at the expense of mating opportunities with additional females. The predicted reproductive success of guarding and nonguarding males was calculated using a model based upon experimentally derived latencies to remating and simulated levels of last male paternity. Guarders outperformed nonguarders when the proportion of offspring sired by the last male (P2) was 0.4 or greater. Data on survival and lifetime mating success were used to evaluate survival trade-offs of postcopulatory riding. Although males sacrificed feeding time to ride on females' backs, there was a positive relationship between the proportion of time males spent riding and their longevity in the patch. These results indicate that postcopulatory riding has no survival costs and indicate that postcopulatory riding can be an effective paternity assurance mechanism even when takeovers are common.

Chemically-mediated pre-mating behavior in two tetranychid species

We used bioassays to evaluate the arrestment response of male twospotted spider mite, Tetranychus urticae Koch, and Banks grass mite, Oligonychus pratensis (Banks) to whole-body extract from conspecific quiescent deutonymphs. We examined the effect of previous behavior on mite response to extract from female quiescent deutonymphs. We also examined male arrestment and guarding behavior in response to 2 extract concentrations and to extract from male quiescent deutonymphs. Male T. urticae and O. pratensis exhibited similar changes in their behavior in response to the different extracts with which we presented them. Males that were guarding quiescent deutonymphs immediately prior to testing spent more time in an untreated 3.5-mm-diameter circle than did males that were previously engaged in other behaviors. However, when nonguarding males were presented with extract of conspecific female quiescent deutonymphs they remained in the stimulus circle as long as guarding males did in an untreated circle. Arrestment duration of nonguarding males increased at 2 higher extract concentrations. The arrestment response was not exclusive to extracts from female quiescent deutonymphs; nonguarding male mites were also arrested by extracts from male quiescent deutonymphs, although for a shorter time. Duration of arrestment was related roughly to size differences between male and female quiescent deutonymphs. Furthermore, males did not show an exclusive preference for guarding conspecific male or female quiescent deutonymphs. It seems unlikely that the arrestant is a specific sex pheromone. Rather, male mites probably use the arrestant as a necessary cue to focus their attention on an individual that may be a suitable mate. Other tactile, visual, and chemical stimuli may then help males to decide whether to remain and assume mate guarding behaviors.

Male size and parental care in the sand goby,Pomatoschistus minutus

Sand goby males guarding eggs from one female without access to food lost 13.9% of their body weight over a caring period of 10 days. This was more than twice the body weight lost by non-guarding males, who had nests but no eggs (weight loss 5.8%). Caring for the eggs therefore imposes an energetic cost on the male. Egg losses in the field were on average 3.3% of the egg mass. Males with egg losses were on average smaller than males without losses and they also had smaller egg masses. If a male was removed and his nest taken by a new male, 31.0 to 100.0% of the original eggs were eaten within 24 hr. In guarding males we never observed hetero-cannibalism. The proportion of time a male spent fanning was positively correlated to his standard length, larger males spending more time fanning. It is concluded that larger males are better fathers.

Arrestment of male twospotted spider mite caused by female sex pheromone

A glass slide bioassay was used to evaluate male twospotted spider mite,Tetranychus urticae Koch, arrestment caused by quiescent deutonymph extract. Males that were guarding quiescent deutonymphs prior to being tested were arrested by a 3-mm-diameter circle of quiescent deutonymph extract; nonguarding males and adult females were not arrested. Extracts of allT. urticae instars tested caused male arrestment, but mean arrestment duration was longest with quiescent deutonymph extract. Arrestment by volatile perception of pheromone and upwind orientation to point sources of extract were not observed. The mono- and sesquiterpene alcohols previously identified as components of the pheromone did not arrest males. HPLC separation of extract resulted in four active fractions; a subtractive bioassay showed that three were essential to elicit maximum male response.

Variable Selection and Size-related Mating Patterns in Natural Populations of Elaphrothrips tuberculatus: A Path Analysis

-In Elaphrothrips tuberculatus, a thrips with male post-copulatory mate guarding, 6 years of study revealed substantial yearly variation in the intensity of sexual selection for large male body size, the standardized size difference between nonguarding males and other nonguarding males, and the magnitude of size-assortative mating. Among years, the intensity of sexual selection for large male body size was positively correlated with the sex ratio (percent males) and the operational sex ratio (ratio of males to females on eggs), and the size difference between sneak and other nonguarding males was positively correlated with the sex ratio. Path analysis of the relationships among variables indicated that: (1) male size-related mating patterns were influenced primarily by the sex ratio; (2) a high magnitude of size-assortative mating was associated with a high sexual selection intensity, a strong tendency for large oviparous females to initiate breeding earlier than smaller ones, a high correlation between the average sizes of males and females among subpopulations (clusters of hanging dead oak leaves), and a low average number of malefemale pairs in subpopulations; and (3) yearly variation in mating patterns may be ultimately caused by yearly variation during the previous summer in amount of breeding, yearly variation during winter in mortality patterns and yearly variation during spring in dispersal rates and the timing of female breeding.

Risks and benefits of lethal male fighting in the colonial, polygynous thrips Hoplothrips karnyi (Insecta: Thysanoptera)

Males of Hoplothrips karnyi (Hood) (Insecta: Thysanoptera), a colonial fungus-feeding thrips, fight each other in defense of communal egg mass sites, where they mate with females that come to oviposit. Fighting males stab each other with their enlarged, armed forelegs and hit each other with their abdomens. Escalated fights occur between large males of similar size. Fights are often lethal; males that died during observations fought more frequently than other males, were stabbed more often and more severely than other males, and were relatively large, but somewhat smaller than their opponents. Large males tend to win fights and guard egg masses, and they secure about 80% of last matings before ovipositions. Guarding males apparently assess female reproductive condition by putting their forelegs partially around females' abdomens; guarding males, but not nonguarding males, mate preferentially with females that have yet to oviposit. Non-guarding males mate with females away from egg masses, sneak matings at egg masses, and occasionally challenge guarding males. Challenges tend to follow matings by non-guarding males at egg masses. Each of four observed or inferred takeovers was followed by the death of the guarding male that lost. Male fighting strategies are discussed in terms of the consistency of lethal fighting with game theory models. Guardin males appear to pursue a classical “hawk” strategy of “escalate until injured or victorious”. This strategy may be advantageous because only large males become guarders, the mating success of guarders greatly exceeds that of non-guarders, and high population viscosity ensures that benefits from killing an opponent accrue directly to gaurders. The occurrence of challenges by large non-guarders implies that fighting ability and resource value asymmetries between males change over time; such changes may result from the energetic costs of guarding, injury to guarding males, or depletion of guarding males' supply of sperm.

Alternative Male Mating Tactics in a Thrips: Effects of Sex Ratio Variation and Body Size

Field observations show that males of Elaphrothrips tuberculatus (Thysanoptera: Phlaeothripidae), a subsocial thrips that inhabits clusters of hanging dead oak leaves, engage in either of two mating tactics, fighting or sneaking that are associated with their body size. Large males fight and guard individual egg-defending females, relatively large nonguarding males fight and challenge guarding males, and relatively small nonguarding males attempt to mate with females while avoiding guarding males. Field collections conducted during 4 years showed that: (1) nonguarding males on the same leaf as guarding males and females (same-leaf' nonguarding males) were significantly smaller than nonguarding males on different leaves (different-leaf nonguarding males) in 3 of 4 years; (2) among years, the size difference between same-leaf and different-leaf nonguarding males was positively correlated with the sex ratio (percent males); and (3) within years, local populations in which at least one of the nonguarding males was a same-leaf male exhibited significantly higher sex ratios. By inference from the observation data, same-leaf males were regarded as sneaks, different-leaf males were temporarily unsuccessful fighters, and male choice of mating tactics depended upon their size and the local sex ratio. Both small body size and a high local sex ratio may be viewed as correlates of a male's inability to secure a female on eggs by searching or fighting. Alternative hypotheses for the data linking male size, location and sex ratio are discussed; relatively small nonguarding males may be intrinsically better at sneaking, or large nonguarding males may fight rather than sneak because of a strong selective association between prior guarding success and aggressiveness. In E. tuberculatus, male mating tactics may be classified as a condition-dependent, reversible strategy, for which the fitness returns of the two tactics are unequal; males sneak when they have an especially low probability of success at winning fights and guarding females.

Variation in Mate Guarding Intensity By Male Purple Martins

AbstractThe frequency with which individual male purple martins (Hirundinidae: Progne subis) guard their mates during forays to gather nest material varies from 0 to 100%. During such forays, guarding males accompany their mates continuously from the time a female leaves the nest site until she returns to the nest site with nest material. Non-guarding males do not accompany females on these collecting forays. Unguarded females are subject to forced extrapair copulation attempts on almost all of their forays to collect nest material. Because this suggested that non-guarding males may have a lowered assurance of paternity relative to guarding males, I asked if mate guarding frequency is directly related to parental care. However, male parental effort, as assessed by feeding rates, was not related to mate guarding intensity. Mate guarding intensity may vary widely among individual male martins since nest site defense may preclude guarding in some and superiority in sperm competition by means other than exclusive access to females may reduce their chances of being cuckolded.