Correlates of reproductive success within alternative mating tactics of the common shrew

Male common shrews (Sorex araneus) adopt two discrete matingtactics. The most successful males, in terms of number of offspringfathered, are those that establish large overlapping home rangesin areas of high female density early in the breeding season.An alternative, less successful mating tactic is to travel longdistances in search of mating opportunities. This study is aninvestigation of correlates of reproductive success for malesadopting these different mating tactics. Reproductive successunder natural conditions was assessed using DNA fingerprinting,and survival of offspring was monitored in the field. The numberof offspring fathered by males with overlapping home rangeswas positively correlated with the number of female ranges overlappedduring the breeding season and with testes mass. The numberof offspring fathered by males that made long-distance movementswas positively correlated with their epididymal sperm counts.It is argued that competitively superior (overlapping) malesachieve high reproductive success by competing to maximize thenumber of females inseminated, whereas those adopting an alternativemating tactic instead compete largely via sperm competition,aiming to maximize insemination success with any particularfemale. There was no significant difference in the fluctuatingasymmetry (FA) of males adopting different mating tactics (FAwas measured as the difference in length of the paired lateralscent glands). Fluctuating asymmetry was not related to thenumber of offspring fathered by males adopting either matingtactic, but was significantly correlated with the proportionof male offspring fathered that survived to sexual maturity.Although apparently not correlated with mating success in thisspecies, FA may reflect some aspect of genetic quality thataffects offspring survival. [Behav Ecol 7: 334–340 (1996)]     

Size Dependent Sexual Selection in Drosophila ananassae

Mate choice based on body size is widespread and can have numerous consequences. We present data, which show the effect of male and female body size on sexual selection in Drosophila ananassae. The relationships between wing size, locomotor activity, mating latency, courtship pattern, fertility and mating success were studied. Mating latency was negatively correlated with wing length and with locomotor activity, while wing length and locomotor activity was positively correlated in males as well as in females. In female- and male-choice, we found that mate choice influenced size-assortative mating by: (1) large and small males preferring to mate with large females, (2) large males successfully competing for large females, leaving small males to mate with small females. Males increased their reproductive success by mating with large and more fecund females. In addition, in pairs of long/short winged flies, long winged flies courted and mated more successfully than short winged flies and they also have longer duration of copulation and more progeny than short winged flies. We found sterile mating in pairs of small winged males and females.     

The mating system of a bee fly (Diptera: Bombyliidae). II. Factors affecting male territorial and mating success

Males of an undescribed bombyliidfly (Comptosia sp.)occupy traditional territories on a Southeast Queensland hilltop, to which females come solely for the purpose of mating. Territorial fights between males involve aerial collisions during which modified spines on the wing margins produce scars on the bodies of opponents. Territory owners and mating males are not different in size or age from the remainder of the male population. Although residency is related to fighting success, the strength of the effect is ambiguous. Consequently, our data do not appear to fit predictions from game theoretical models for fighting protocol. Hilltop males lacked the extensive population variation typically found in territorial species, and thus, the presumed advantages of traits such as large size may be suppressed. Hilltop males were larger than males at a nonhilltop, resource-based mating site and the possibility of alternative mating tactics is discussed.     

Competition for landmark territories among male Polistes canadensis (L.) (Hymenoptera: Vespidae): large-size advantage and alternative mate-acquisition tactics

Alternative male mating tactics of insects at landmarks (leks)have only rarely been investigated. Some males of the paperwasp, Polistes canadensis (L.), were territorial at small treesalong the crests of dry ridges in Santa Rosa National Park,Costa Rica. Territories did not contain nests or resources forwhich females foraged. Contrary to other "hilltopping" species,male P. canadensis competed most intensely for territories insaddles along these ridges rather than at the highest points.Nonterritorial males patrolled small areas of the ridge line,following a path that took them to a number of territories.Many males switched between territoriality and patrolling, suggestingthat both size-related tactics belong to one conditional strategy.Males that were territorial on 2 or more days were larger thanthose that were territorial on only 1 day, and these in turnwere larger than permanent patrollers. Moreover, the mean sizeof territorial males was positively correlated with two measuresof territory attractiveness, suggesting that larger males monopolizepreferred sites. Mean age of territorial males was also relatedto territory attractiveness, but males of intermediate age claimedthe most attractive territories.     

Fluctuating asymmetry, size and mating success in males of Ischnura elegans (Vander Linden) (Odonata: Coenagrionidae)

Fluctuating asymmetry (FA) is thought to be an indicator of developmental stability and negatively related to male mating success in many animal taxa. We investigated the relationships between mating success of males, body size and FA for both wing length and number of setae on the legs in the damselfly Ischnura elegans. Males were classified as mated or unmated at the time of sampling. Fluctuating asymmetry, expressed as right-left differences, showed normal distributions without evidence of directional asymmetry or antisymmetry. Univariate analyses showed a significant negative correlation between size and mating success, and significant negative correlations between FA and mating success for both characters. On the other hand, with a multivariate analysis, new to studies on FA, the effect of body size was still significant but FA did not reach significance for either character. We conclude that the multivariate analysis should be used to assess the role of the different factors affecting mating success. Copyright 2000 The Association for the Study of Animal Behaviour.     

Male Age,Copulation Duration and Insemination Success in Mystacides azurea (Leptoceridae,Trichoptera)

Time in copula in the swarming caddis fly Mystacides azurea L. (Trichoptera: Leptoceridae) ranged from 0.33 to 44.5 min. It increased with male age (wing wear) and male dry weight, but was independent of male and female size (forewing length), female wing wear and number of eggs in the females. Older males failed to transfer sperm during copulation more frequently than did younger ones. It is suggested that females benefit by interrupting prolonged copulations if sperm is not transferred rapidly, since being in copula might increase the risk of predation. Alternatively, young and old males follow different mating tactics; old males have a lower chance to acquire new mates and they do better by monopolizing a female, once they get one, by prolonging the copulation.     

THE EFFECTS OF BODY SIZE ON MATING FEATURES IN A FIELD POPULATION OF THE HERMAPHRODITIC SEA HARE APLYSIA KURODAI BABA, 1937 (GASTROPODA: OPISTHOBRANCHIA)

Mating behaviour of the hermaphroditic sea hare Aplysia kurodaiBaba was observed in the field to investigate the effects ofbody size on various mating features. Compared with small individuals,large gastropods mated with more partners both as males andas females, and also with larger partners (size-assor-tativemating). Large gastropods also mated more frequently as femalesbut not as males, and tended to be selected as female matingpartners more often than small ones by neighbouring individualsbut not as male partners. All these results suggest some matingadvantage of large individuals over small ones as females, probablybecause of the preference by male partners for large femalepartners. At the same time, the results suggest that the matingadvantage of large size as males may be limited, if any. Thepreference for large female partners is also consistent withthe fact that their mating was longer than that of small ones.The greater advantage of large size in mating as females, thanas males, means that sexual selection at mate determinationacts more strongly on female size than on male size and thatthe direction of total sexual selection at mating is probablyreversed in this hermaphrodite (Received 27 November 1995; accepted 8 February 1996)     

Variation in energy reserves and role of body size in the mating system of Anopheles gambiae

Anopheles gambiae mates in flight. Males gather at stationary places at sunset and compete for incoming females. Factors that account for male mating success are not known but are critical for the future of any genetic control strategy. The current study explored variations in nutritional reserves (sugars, glycogen, lipids, and proteins) in wild‐caught swarming and resting males and evaluated the effect of body size and wing symmetry on male mating success. Our results showed that glycogen and sugar reserves are mobilized for flight. Males consume proportionally 5.9‐fold as much energy derived from sugars in swarming activities than when they are at rest. Mated males were on average bigger than unmated ones (P<0.0001). A strong correlation between the left and right wings in both mated and unmated males was found and additional analysis on fluctuating asymmetry did not show any indication of mated males being more symmetrical than unmated ones. The distribution of wing size of mated males was focused around a central value, suggesting that intermediate size of males is advantageous in the An. gambiae mating system. The results are discussed in the context of sexual selection.     

Male Reproductive Tactics in an Explosive Breeding Toad Population

American toad (Bufo amencanus) males use one of two differentreproductive tactics. Some males are stationary and call. Othersare silent and mobile. Based on field studies, I developed acomputer program that simulates the behavior of females andmales to determine the probability of mating success of malesengaging the different tactics and the factors that effect malereproductive success. Field studies indicate that non-calling males can be successful.Non-calling males were more numerous and smaller than callingmales. Population size changed greatly both between and withinnights. Contact rates for non-calling males were greater thanthose for calling males. The results of the preliminary simulations indicate that malemating success is a function of the population size and theoperational sex ratio. In small populations, contact rate hasno effect on male success. The effect of contact rate on malesuccess has not been tested in large populations. In large populations,mating success is also a function of the ratio of calling tonon-calling males. Generally, in small populations (n > 20)calling males are more successful than non-calling males. Inlarge populations (n > 40) the success of noncalling malesis equal to or greater than the success of calling males.     

Group spawning results from the streaking of small males into a sneaking pair: male alternative reproductive tactics in the threespot wrasse Halichoeres trimaculatus

In many protogynous wrasses, large males with bright coloration (terminal phase males, TP males) establish mating territories and pair-spawn with females. In contrast, small primary males with drab coloration (initial phase males, IP males) are non-territorial and adopt three alternative reproductive tactics—group spawning, streaking, and sneaking. We investigated how IP males of the threespot wrasse Halichoeres trimaculatus use these tactics in different situations. The mating frequency of the IP males was positively correlated with their courtship frequency, but not with their body size. Larger IP males tended to attack the smaller ones at the mating sites. This indicates that the larger IP males attempted to exclude the smaller ones from mating with the intention of minimizing the number of IP males involved in group spawning and ultimately leading to pair spawning (sneaking). However, the larger IP males were unable to completely exclude the smaller males because the intensity of the attack by the larger IP males was weak. Consequently, the smaller IP males could easily streak into the sneaking of larger IP males, thereby resulting in group spawning.     

Body size and mating success inDrosophila willistoni are uncorrelated under laboratory conditions

Mating activity and wing length were investigated in the F₁ progeny ofDrosophila willistoni females collected in the field to examine any possible relationship between body size and mating success. The flies were observed in a mating chamber under laboratory conditions. No significant differences in wing length were observed between copulating and noncopulating flies, and there was no significant correlation between wing length and copulation latency for both males and females. These results therefore suggest that the commonly accepted view that large body size is positively correlated with mating success inDrosophila does not always hold true. The results support the view that the extent of environmentally induced variation in body size may be an important factor in determining whether an association between body size and mating success is observed inDrosophila species.     

Size and mating success in males of the western harvester ant,Pogonomyrmex occidentalis (Hymenoptera: Formicidae)

Mating success in males of the lek mating ant species,Pogonomyrmex occidentalis, increases with increased body size. We estimated the magnitude of the selection coefficients on components of size by collecting males in copula and comparing their morphology to that of males that were collected at the lek but that were not mating. Four characters, body mass, head width, wing length, and leg length, were measured for a sample of 225 mating and 324 nonmating males and 225 females. Significant direct selection favors increased wing length and leg length. Multiple regression of transformed variables (principal components) indicated that the increased mating success of larger males is a function of all four characters. We found no evidence of positive assortative mating on the basis of any individual character or on the multivariate general size variable (the first principal component).     

SEXUAL SELECTION IN THE BARN SWALLOW (HIRUNDO RUSTICA). IV. PATTERNS OF FLUCTUATING ASYMMETRY AND SELECTION AGAINST ASYMMETRY

The patterns of variation in fluctuating asymmetry were studied in four morphological characters of the barn swallow Hirundo rustica. The level of absolute and relative asymmetry was larger in the secondary sexual character “outer tail length” than in three nonsexual morphological traits (wing, central tail, and tarsus length). The extent of individual asymmetry in outer tail length was negatively correlated with tail-ornament size, whereas the relationship between asymmetry of all other morphological characters and their size was flat or U-shaped. Asymmetry in outer tail length was unrelated to asymmetry in other morphological characters, whereas asymmetries in the length of wing, central tail, and tarsus were positively correlated. Male bam swallows exhibited larger asymmetry in outer tail length than females. Asymmetry of most morphological traits exhibited intermediate repeatabilities between years, with the exception of male and female outer tail length, which were highly repeatable. Tail asymmetry of offspring weakly, though significantly, resembled that of their parents. Asymmetry in wing and outer tail length was also significantly related to several fitness components. Male barn swallows that acquired a mate were less asymmetric in wing and outer tail length than unmated males. Females with more asymmetrical tails laid eggs significantly later. Annual reproductive success was unrelated to fluctuating asymmetry. Male barn swallows that survived were less asymmetric in wing and outer tail length than nonsurvivors, whereas female survivors were less asymmetric in outer tail length than nonsurvivors. These results suggest that levels of fluctuating asymmetry in barn swallows are associated with differences in fitness.     

An experimental approach to altering mating tactics in male horseshoe crabs (Limulus polyphemus)

Alternative reproductive tactics are often correlated with phenotype, density, environment, or social context. Male horseshoe crabs(Limulus polyphemus) have two mating tactics that are associatedwith phenotype. Males in good condition arrive at the nestingbeach and spawn while attached to females, whereas those inpoorer condition come ashore unattached and crowd around thenesting couples as satellites, fertilizing eggs through sperm competition. The correlation between mating tactic and phenotypemay be due to males choosing tactics based on condition, orit may be that males that have not found a female choose tocome ashore as satellites. To distinguish between these twopossibilities, I conducted an experiment on male horseshoe crabsin the field at Seahorse Key on the northern Gulf coast ofFlorida. I prevented males from attaching to females by placingsmall plastic bags over the claws they use to attach. The resultsshowed that males in poor condition came ashore as satellites,whereas males in good condition remained at sea. This meansthat mating tactics are cued by information about the male'scondition and not about whether he found a female. The evolutionof phenotype-correlated mating tactics can be represented bya model in which the fitness of each tactic changes with conditionand fitness curves cross. I hypothesize that male horseshoecrabs in good condition have higher fitness when attached and that males in poorer condition to better when unattached.     

Sexual Selection of Zorion guttigerum Westwood (Coleoptera: Cerambycidae: Cerambycinae) in Relation to Body Size and Color

Zorion guttigerum is a flower-visiting longhorned beetle endemic to New Zealand. Sexual selection of this species in relation to the body size and color form of different sexes was investigated in the field. The population sex ratio, based on censuses of feeding and mating sites (flowers), is male-biased. Females are significantly larger than males. Both sexes have antennae of similar length but the antennal length relative to the elytral length is greater in males than in females, and the antennal length of males increases more with an increase in body size than that of females. Both sexes have dark blue (DB) and yellowish-brown (YB) individuals. Both pair-bonded and solitary males are similar in elytral and antennal length. In pair-bonded males, DB individuals are significantly more numerous than YB ones, but in solitary males, the number of both color forms is similar. Males tend to have territory protection behavior, fighting with and chasing away rival males from feeding and mating sites. Larger males usually win the fight but the size-dependent fighting advantage does not translate into mating success. Male color plays an important role in mating success, with DB males having a significantly better chance to mate than YB males. Furthermore, male body size and color also have interactions in mating success: males of DB color morph obtain a greater mating advantage according to body size. Pair-bonded females are significantly larger and have longer antennae than solitary females, suggesting that males prefer larger females for mating. In addition, females of DB color morph with longer antennae are also preferred by males for mating. The significance of these findings is discussed.     

Horn asymmetry and fitness in gemsbok, Oryx g. gazella

The relationship between fluctuating asymmetry in horns of gemsbok(Oryx g. gazella) and a number of fitness components was determinedin a field study in Etosha National Park, Namibia. The lengthand width of horns and skull length demonstrated fluctuatingasymmetry. Both males and females with asymmetric horns werein poorer condition than symmetric individuals. Individualsof both sexes with symmetric horns more often won aggressiveinteractions at waterholes. Although symmetric individuals spentmore time in dense vegetation, their vigilance rate was nothigher than that of asymmetric individuals. Territorial, singlemales had more symmetric horns than males in herds, suggestingthat mating success was inversely related to horn asymmetry.Females with symmetric horns more often had calves than asymmetricfemales. Horn asymmetry thus appears to reliably reveal phenotypicquality as demonstrated by a suite of fitness components.[BehavEcol 7: 247-253 (1996)]     

Is bigger better? Male body size affects wing‐borne courtship signals and mating success in the olive fruit fly,Bactrocera oleae (Diptera: Tephritidae)

Variations in male body size are known to affect inter‐ and intrasexual selection outcomes in a wide range of animals. In mating systems involving sexual signaling before mating, body size often acts as a key factor affecting signal strength and mate choice. We evaluated the effect of male size on courtship displays and mating success of the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae). Wing vibrations performed during successful and unsuccessful courtships by large and small males were recorded by high‐speed videos and analyzed through frame‐by‐frame analysis. Mating success of large and small males was investigated. The effect of male–male competition on mating success was evaluated. Male body size affected both male courtship signals and mating outcomes. Successful males showed wing‐borne signals with high frequencies and short interpulse intervals. Wing vibrations displayed by successful large males during copulation attempt had higher frequencies over smaller males and unsuccessful large males. In no‐competition conditions, large males achieved higher mating success with respect to smaller ones. Allowing large and small males to compete for a female, large males achieve more mating success over smaller ones. Mate choice by females may be based on selection of the larger males, able to produce high‐frequency wing vibrations. Such traits may be indicative of “good genes,” which under sexual selection could means good social‐interaction genes, or a good competitive manipulator of conspecifics.     

Why make daughters larger? Maternal sex-allocation and sex-dependent selection for body size in a mass-provisioning wasp, Trypoxylon politum

Mass-provisioning wasps package maternal investment into broodcells, sealed structures that contain all the provisions necessaryfor an offspring's growth and development. Optimal sex-allocationtheory predicts that if maternal provisions determine the sizeof each offspring, and the amount of provisions available toeach offspring varies, females should allocate well-stockedbrood cells to the sex that benefits most from being large.I tested this hypothesis using observations of organ-pipe wasps,Trypoxylon politum, and dissections of their nests. A Mississippipopulation of T. politum was intensively studied from 1993 to1995. This population fit the assumptions of optimal sex-allocationmodels by Green and Brockmann and Grafen. Female weight at emergencewas 1.29 times that of males, and wing length was 1.15 timesthat of males. This discrepancy in size occurred because thevolume of parental provisions strongly influenced adult bodysize, and better-stocked brood cells were preferentially allocatedto daughters. Brood-cell volume correlated with both wing lengthand weight at emergence in both sexes, and the chance that agiven brood cell contained a female offspring increased withincreasing brood-cell volume. Fitness was positively relatedto body size for females, but I found no evidence of an advantageto large males. Although there was evidence of stabilizing selectionfor male wing length in one year, there was no evidence of anincreasing relationship between body size and fitness (directionalselection) for males in either 1993 or 1994. Female fecunditywas positively related to body size in both years, indicatingthat larger females have increased reproductive success. Therate at which females provisioned brood cells was also correlatedwith body size. Observed patterns of investment in brood cellsare quantitatively consistent with the predictions of optimalsex-allocation theory, but certain aspects of female provisioningbehavior suggest females are not following a single "optimal"strategy. Patterns of provisioning were variable among differentfemales at the study site during the same year. Large femalestended to produce larger offspring. Although Brockmann and Grafen'smodel predicts a single, population wide "switchpoint" fromthe production of male to female offspring, there was no evidencefor such a switchpoint     

Alternative reproductive tactics and courtship in the common goby

In the marine common goby Pomatoschistus microps , males either build nests and attract females to spawn or act as sneakers, forcing themselves into other males' nests during mating, to fertilize some of the eggs in the clutch. The reproductive tactics of small males were studied in the presence of surplus nest material and an excess of gravid females, while a larger, nestholding male spawned with a female. Of 24 small males, 13 only attempted to sneak, seven only courted females and/or spawned in their own nest, and four performed both behaviours. The small males who attracted females successfully were significantly larger than the ones who failed to do so. Females had been courting the small male more often when he subsequently spawned in his own nest, than when he did not get a female. The small males did not court the females very frequently, and their courtship rate did not depend on whether or not they attracted females. Instead, female courtship behaviour may be a cue for a male either to spawn as a nest holder or become a sneaker. The study pointed out the importance of female behaviour for male reproductive tactics, which could be more important in fish than is known currently.     

Mechanisms of sexual selection operating on body size in the mosquitofish (Gambusia holbrooki)

Collections in two natural populations of the mosquitofish,Gambusia holbrooki, were made to determine whether the sexesassociated nonrandomly based on body size, and laboratory experimentswere performed to identify mechanisms that could generate theobserved field patterns of association. In both populationslarger females were associated with larger males. However, thesize distributions of males caught with and without femaleswere not different. Both gravid females and females that hadreleased broods within the previous 24 h spent more time nearlarger males in laboratory choice experiments. In contrast,males did not discriminate between females on the basis of sizeor reproductive status in laboratory choice experiments, andmales did not attempt relatively more copulations with largerfemales when one male was allowed to freely interact with twofemales. Body size differences and aggressive interactions betweenmales did influence the access of males to females, with largermales attempting more copulations with females when two maleswere allowed to freely interact with one female: aggressiveinteractions between males were frequent when males differedby < 1.0 mm standard length but were rare when males differedby>5.0 mm standard length. These results indicate that femalechoice for larger males could contribute to generating the nonrandomassociations between the sexes that were observed in these twopopulations and that interactions between males in the vicinityof females may additionally increase the mating advantages oflarger males.