Effect Of Male Size Research Articles

Reproductive ecology and territorial behavior of Boana goiana (Anura: Hylidae), a gladiator frog from the Brazilian Cerrado

Anuran males and females adopt different reproductive and behavioral strategies in different contexts. We investigated the reproductive ecology and territorial behavior of the treefrog Boana goiana (B. Lutz, 1968) from the Brazilian Cerrado. We hypothesized that competitor density/proximity would increase the behavioral responses of B. goiana males, and that mating would be assortative. We also tested if the number of eggs correlates with female size and if there is a trade-off between clutch size and egg size. We conducted two territoriality experiments to test the effects of male size, competitor proximity and competitor density. Larger males called more in the presence of a second male. In the second experiment, the largest males emitted more calls and the distance to the nearest male increased as resident males called more. In both experiments, the number of calls was influenced by either male size or spacing between males. Some males behaved as satellites, probably to avoid fights. Our analyses indicate that females choose males with similar sizes to their own, corroborating our hypothesis of size-assortative mating. We found no relationships between female size and clutch size/volume, and between egg size and number of eggs per clutch. We also report multiple spawning for this species. The low incidence of physical combats and the spacing pattern indicate that this species relies almost solely on calls to resolve contests, which could be explained by low motivation, or simply because males avoid combats to decrease injury risks. Thus, acoustic or even multimodal communication seems crucial for social interactions of B. goiana.

Sperm competition in golden cuttlefish Sepia esculenta: The impact of mating order and male size

Sperm competition, as the last form of male competition prior to fertilization, is an important component in the reproductive and evolutionary biology of polyandrous species. Golden cuttlefish (Sepia esculenta) is a commercially important annual cephalopod, in which females often mate with multiple males during their mating season and maintain viable sperm in their sperm storage organs for a long time. This multiple-mating system leads to male competition and ultimately sperm competition. To explore the mechanisms of sperm competition in cuttlefish, a laboratory study was conducted using three experimental approaches. First, two similar-sized males were introduced to sequentially mate with a single female (experiment 1), to investigate mating order effects on paternity. Thereafter, a four-male experiment was run (experiment 2), which again tested for mating sequence on paternal contribution. Finally, to test whether male size is a factor affecting paternity, we compared the paternity of two different-sized males that were sequentially mated with a single female (experiment 3). The paternity of the offspring was analyzed using six microsatellite DNA markers on fertilized eggs. The results revealed last-male sperm precedence in all experiments, and no effect of male size was detected. For the two-male experiment, the last male to mate had a progeny share (P2) of 42.86%–61.90%. For the four-male experiment, the last mated male had the highest progeny share (P4) with a proportion of 35.56%–43.75%. Even with differential male sizes in the two-male experiment, the last mated male retained the highest progeny share (P2, 58.33%–91.67%). This study shows a consistent pattern of last-sperm advantage across different experiments and contributes to growing research on cephalopod mating systems. Proper mating schemes should be considered during seedling production for S. esculenta to ascertain efficient resource use and genetic diversity in produced offspring.

Does Size Matter? Mate Choice in Two Lekking Flies.

For insect pests controlled through the Sterile Insect Technique (SIT), which consists in the mass production, sterilization, and release of target insects into affected areas, sterile male mating success with wild females is the key that will reduce population levels in the next generation. Male size is assumed to be important for mating success, but often without any concrete evidence or confounded by other parameters. Here, we evaluated male size and its interaction with male origin (laboratory or wild) on female choice for two lekking species controlled through SIT, Anastrepha obliqua (Macquart) and Anastrepha ludens (Loew) (Diptera: Tephritidae). In field cages, we tested wild females mating with: large wild males competing against small wild males; large wild males against small laboratory-sterile males; and large laboratory-sterile males against small wild males. We found evidence of large male advantage for A. obliqua but no effect of male size on mating competitiveness for A. ludens. For A. obliqua large wild males had a greater mating success over small laboratory males, yet large laboratory males secured a similar amount of copulations than small wild males. For A. ludens, there was no effect of male size on mating success. We discuss why A. obliqua is sensitive to size and origin while no effect was seen in A. ludens. SIT programs should not assume that male mating success is dependent on a large size. Alternatively, when an advantage exists for large males, mass-rearing programs should stride to produce and release large males.

Spermathecal Filling in Aedes aegypti and Aedes albopictus: Effects of Female and Male Body Sizes and Species.

The mosquitoes Aedes aegypti (L.) (Diptera: Culicidae) and Aedes albopictus (Skuse) (Diptera: Culicidae) are ecologically similar species that have evolved independently in their native ranges, Ae. aegypti in Africa and Ae. albopictus in Asia. Where their invasive ranges overlap, interspecific mating is facilitated by both species swarming to mate around bloodmeal hosts during daylight. Here, we test hypotheses to account for variation in spermathecal filling in females of Ae. aegypti and Ae. albopictus, particularly, the effect of mosquito size on the number of spermathecae containing sperm after intraspecific and interspecifc matings of these two species. Results show that significantly more spermathecae contained sperm in large than in small Ae. albopictus females, but there was no effect of Ae. aegypti female body size on the average number of spermathecae filled. Among inseminated females, there was no effect of male size or cross-type on number of spermathecae with sperm. Differences in the effect of female size on the number of spermathecae that store sperm in Ae. aegypti and Ae. albopictus imply differences in the mating biology of these two species.

Spatial and temporal patterns of nest distribution influence sexual selection in a marine fish

In many species, the natural distribution of material resources important for reproduction can profoundly impact reproductive success among individuals and, hence, the opportunity and intensity of sexual selection. Here, we report on a field‐based experiment investigating the effects of nest aggregation on sexual selection in a fish, the sand goby Pomatoschistus minutus. We found that the distribution of potential nests (sparse versus aggregated nest treatments) affected patterns of nest colonization and reproductive success. Specifically, in the treatment with aggregated nesting resources, a greater proportion of nests remained unoccupied by sand goby males. Although the size of nesting males did not differ between treatments, eggs accumulated more rapidly when nests were sparsely distributed. We found that the opportunity for selection decreased over time with the accumulation of eggs in the nests in both the aggregated and sparse treatments. Moreover, the effect of male size on reproductive success was influenced by an interaction between nest distribution and time, with the selection gradient being highest right after nest colonization when nests were aggregated, while the opposite pattern was observed in the sparse nest treatment. Such findings highlight the vital role that environmental and social factors can play in determining the importance of male phenotypic traits (in this case, male size). More broadly, our results also underscore how the natural distribution of resources, both in space and time, can impact the strength of sexual selection acting on wild animal populations.

Temporal dynamics of intersexual conflict and the effect of male quality on female fecundity in the marine isopod Cleantiella isopus

Crustacean males grasp and/or guard females before copulation to ensure mating, but females typically resist males during pair formation. The benefit of resistance for females might allow (1) females to optimize mate quality, or (2) to avoid costs incurred during guarding. However, it has not been fully investigated which benefits actually improve female fitness. Here we investigated female resistance, temporal dynamics of intersexual conflict during reproduction, and the effect of male size and male mating frequency on female fecundity in the marine isopod,Cleantiella isopusto examine the relative importance of the two mechanisms mentioned before. Females resisted even after they had become receptive. Females which mated with small males showed lower fecundity than the ones with large males, and small males were frequently unable to form pairs. These results suggest that female resistance ofC. isopusagainst males can function as a way to optimize mate quality.

Male mating costs in a butterfly that produces small ejaculates

AbstractIn many insects, ejaculate size is positively related to male fitness, although the production of large ejaculates entails physiological costs that can result in decreased male longevity. Ejaculate production costs have been studied in butterfly species because males generally produce large ejaculates that are rich in resources. However, lepidopterans show interspecific variation with respect to relative investment in ejaculates (i.e. percentage of male body weight invested in ejaculates) that could influence the magnitude of costs. The physiological costs of ejaculate production are expected to differ between males with different amounts of resources stored. The effect of male size (an estimate of the amount of resources stored) on ejaculate production and on survivorship costs of multiple mating is studied in males of Leptophobia aripa Boisduval (Pieridae), the butterfly with the smallest relative investment in spermatophores recorded to date (0.31%). ‘Small males’ produce smaller spermatophores, although male size has no effect on ejaculate size (spermatophore + accessory substances), indicating that ‘small males’ make a relatively larger investment in the production of accessory substances. The results indicate that L. aripa males are able to modify the relative amount of resources invested in ejaculate production. Multiple mating has a negative effect on male longevity and this effect depends on male size: in comparison with virgin males, the longevity of ‘small males’ decreases after just one copula, whereas the longevity of ‘large males’ decreases after two copulations. The possible reasons why ‘small males’ invest relatively more resources in ejaculate production, despite the fact that they pay larger costs, are discussed.

Effects of Male Size on Searching Behaviors in the Sun Dance ofBembix

Males of solitary wasp species are faced with the task of locating potential mates, a task made more difficult by inconspicuous females and a landscape seemingly devoid of landmarks. Males may employ a variety of strategies to locate females. In this study, we test for variation among males within the sun dance of Bembix. We show that males of Bembix americana spinolae Lepeletier behave differently within the sun dance and that these differences can be predicted by the size of the male. We show that large males spend more time at “rest” and require a greater number of male-male contacts to be displaced from rest than small males. This difference in mate location strategy, however, appears to be density dependent, as large and small males in small aggregations exhibit no difference in the strategies they employ.

Effects of Age and Size on <I>Anopheles gambiae</I> s.s. Male Mosquito Mating Success

Before the release of genetically-modified or sterile male mosquitoes in an attempt to control local populations of malaria vectors, it is crucial to determine male traits involved in mating success. The effects of male size and age as determinants of male mating success in Anopheles gambiae s.s. were measured in the field and under laboratory conditions in Burkina Faso. First, the body sizes (estimated by wing length) of mating, swarming, and indoor-resting male mosquitoes were compared over a 3-yr period (2006-2009) from July to October in Soumousso and Vallée du Kou, two villages in western Burkina Faso. Second, the age structure of swarming and resting male mosquitoes were characterized based on the number of spermatocysts and the proportion of sperm in the reservoir of wild-caught male testis. Third, male age effects on the insemination rate of female An. gambiae were investigated in the laboratory. The mean size of males collected in copula was significantly larger than the mean for swarming males and indoor-resting males. The optimum male age for successful insemination of females was 4-8 d. These results suggest that male size is an important trait in determining male mating competitiveness in the field. Although age was not found to be a significant factor in mating competitiveness, it was significantly correlated with swarming behaviors in the field and insemination success in the laboratory. The implications of these results in terms of sexual selection in An. gambiae and vector control programs are further discussed.

Context-dependent male mate choice: the effects of competitor presence and competitor size

Differences in the intensity of male–male competition for high- and low-quality females affect their value as mates. This can favor the evolution of mating preferences that vary with inherent male competitiveness and/or context-dependent mate choice. In the eastern mosquitofish (Gambusia holbrooki) we investigated how a male’s choice of mate is influenced by his absolute size when alone (baseline mating preference) and by the presence and relative size of a competitor (context dependent). In standard 2choice mating trials, we compared the time in association with the larger of 2 females in: 1) the absence of a rival; 2) the presence of a same-sized rival, and 3) the presence of a different-sized rival. We predicted which female the focal male would choose based on his estimated reproductive success. In all 3 social contexts, large and small focal males spent significantly more time with large females, but large males had a stronger association bias, indicating an effect of male size (competitiveness) on male mating preference. In contrast, neither the presence of a competitor nor his relative size affected the time the focal male spent with the large female. There was therefore no evidence that males facultatively adjust mate choice decisions to avoid competitors. This suggests that males do not maximize their expected reproductive success in the context of the current social setting. Key words: eastern mosquitofish, Gambusia holbrooki, male–male competition, mating preferences, sexual selection. [Behav Ecol]

Effects of male size and female dispersion on male mate-locating success in Nephila clavipes

The reproductive success of sexually reproducing organisms depends on their capacity to locate potential partners. Research on the mating systems of web-building spiders, like other terrestrial invertebrates, has focused around male courtship and the signalling behaviours that facilitate copulation. In contrast, both mate searching and mate location behaviours are largely ignored and rarely quantified in field studies. We conducted a series of field removal experiments to explore the effects of male body size and female dispersion on mate locating behaviour of the golden orb-weaving spider (Nephila clavipes). The number of males that arrived on females’ webs was influenced by travel distance, male body size, male body weight and female dispersal. More males returned to webs that were closer to the release point; smaller males experienced a greater weight loss; and larger numbers of males arrived at webs where males had been previously present. Female dispersion influenced the size but not the number of arriving males: males were no more likely to arrive at solitary than aggregations of webs, but males arriving at solitary webs were typically larger than those arriving at aggregations. We discuss the implications of various male traits that could act as selective pressures on male mate location and mate searching behaviours.

Daily production of spermatophores, sperm number and spermatophore size in two eriophyoid mite species

Under dissociated sperm transfer, (non-pairing) males deposit spermatophores on a substrate, while females seek spermatophores and pick up sperm on their own. Spermatophore expenditures of non-pairing males should be high, due to the increased uncertainty of sperm uptake by a female. In this study I examined spermatophore expenditures in two eriophyoid species that differed in the degree of dissociation between sexes: (1) Aculus fockeui (Nalepa and Trouessart) males rarely visit quiescent female nymphs (QFNs), and mostly deposit spermatophores all over the leaves, whereas (2) Aculops allotrichus (Nalepa) males guard QFNs for many hours and deposit several spermatophores beside them. Males of both species were collected from the field and tested in solitude. Aculus fockeui males deposited on average 19.1 spermatophores per day, whereas A. allotrichus deposited only 3.6 spermatophores per day, and had a very large coefficient of variation. Males and spermatophores of A. allotrichus were significantly smaller and contained less sperm than those of A. fockeui. In both eriophyoids, spermatophore size was fitted to the size of female genitalia and the height of females. The ratio between the diameter of spermatophore head and the width of a female genital coverflap was 0.6, whereas the ratio between the female leg and the length of spermatophore stalk was 0.5. Several factors could be responsible for the discrepancy in spermatophore expenditures between species. Among other factors, the effects of male size, male reproductive strategy and female genitalia size on spermatophore output and size of spermatophores are discussed.

Sperm limitation: possible impacts of large male-selective harvesting on reproduction of the coconut crab Birgus latro

For many biological resources, larger males are more likely to be harvested than smaller ones. In such harvested populations, the remaining males are relatively small and participate in more matings than in pristine populations. Because the number of sperm passed to females generally decreases with decreasing male body size and increasing male mating frequency, the reproductive success of females in populations subjected to such harvesting patterns can be restricted due to sperm limitation. The Japanese population of the coconut crab Birgus latro is typically subject to large male-selective harvesting, which may be one of the causes of the presently observed B. latro population decline. To examine the impact of harvesting on coconut crab populations, the effects of male size and mating frequency on male reproductive potential (number of ejaculated sperm and fer- tilization rate), sperm recovery rate, and the number of sperm received by females in a harvested population were investigated. Larger males provided females with larger numbers of sperm and achieved higher fertilization rates. Although the number of ejaculated sperm decreased with increas- ing mating frequency regardless of male size, larger males always passed more sperm to successive mates than smaller ones. The number of used sperm did not increase even after 30 d, suggesting a low sperm recovery rate. More than half of the females collected after the beginning of the reproduc- tive season had very low numbers of sperm. These results suggest that the reproductive rate of the coconut crab has declined due to females suffering from sperm limitation.

Influence of Adult Male Size on Fecundity and Progeny Size in Callosobruchus maculatus (Fabricius) [Coleoptera: Bruchidae

The effect of male size on fecundity and progeny size in Callosobruchus maculatus (Fabricius) was studied under ambient laboratory conditions in Akure, Nigeria. The highest number of eggs (83.8) was laid when a big male was mated with a big female. This was followed by the 66.3 eggs laid when a big male was mated with a small female. Pairing involving a small male and a big female, and a small male and a small female produced lower numbers of eggs (40.0 and 34.4, respectively). Similarly, the highest number of progeny (57.4 adults) was produced when a big male was mated with a big female. This was followed by the progeny produced (43.4 adults) when a big male was mated with a small female. Pairing involving a small male and a big female produced 20.7 adults; comparable number for the small male and small female pair was 20.0 adults. Unmated males were observed to live longer than mated males. Daily loss in weight was significantly higher (P< 0.05) in mated than in unmated males.

Azorean rock-pool blennies produce size-dependent calls in a courtship context

Male calling or singing behaviour often plays a crucial role in competition among males and attraction of females. We studied the occurrence of male calls in a paternal nest-guarding fish, the rock-pool blenny. We found that males often produced calls when a female entered their nest burrow and during her visit inside the burrow. The dominant grunt-like part of these calls has a fundamental frequency of about 30 Hz and generally contains one to six harmonics. This harmonic component is typically preceded by a short introductory component and often followed by an even shorter terminal component, both of relatively low amplitude and irregular spectral composition. The fundamental frequency differs consistently between males and is negatively correlated with male size. Consequently, spectral features of the calls may be used in female mate choice during the female's decision to stay in a burrow and spawn. Not all males that were observed during a female visit produced calls, nor did calling males call during all female visits. The number of calls during a visit varied within and between males and ranged from 1 to 13. Calling may express some male mate preference when calls are selectively produced during visits of preferred large females. However, we did not find any evidence for differences in calling activity towards three female size classes, nor was there an effect of male size. This is one of the first reports in the literature on the use of sounds in blenny courtship behaviour and adds to a growing body of evidence revealing the communicative importance of acoustic signals in a wide variety of fish taxa.

Male-male competition selects for delayed sex change in the protandrous shrimp Pandalus latirostris

In most protandrous species, male size advantage is generally regarded as unimportant in determining the timing of protandrous sex change. In pandalid shrimp, the size/age of male sex change often fluctuates among years and populations, but the adaptive significance of late reversing males (LRMs) is not well understood. This study experimentally examined the adaptive significance of LRMs in the protandrous pandalid shrimp Pandalus latirostris Rathbun. Field and laboratory studies were carried out in August–September of 1998–2002 on P. latirostris in Notoro Lagoon, Japan (44°03′N; 144°10′E). Mature females that had molted (i.e. mate receptive) were tethered in the field and their mating behavior with wild males was observed. Copulations occurred with a single male at a time, although other males could sequentially mate with a tethered female. Because tethered females rejected male approaches, males had difficulty transferring their spermatophores. In the laboratory, males copulated with non-tethered, recently molted females for only 15 min after molting. Recently molted females are wary of potential predators, since their soft exoskeleton makes them particularly vulnerable. Fast access by males enhanced fertilization success in this shrimp. The effect of male size on mating success in the laboratory was examined. Both small and large males successfully inseminated females in the absence of competitors. In experiments where large, medium, and small males competed for a female, however, larger males guarded females longer than smaller males, until the female molted and became receptive. Moreover, large males were more successful at copulating once molting occurred. These results imply that male-male competition drives delayed sex change in some situations.

MORPHOMETRIC TRAITS AND SEXUAL SELECTION IN MEDFLY (DIPTERA: TEPHRITIDAE) UNDER FIELD CAGE CONDITIONS

The effects of male size and other morphometric traits as determinants of male mating success were evaluated under field cage conditions. Males of the laboratory Seib6-96 strain were released into field cages with males and females of a wild population from the Patagonian region. Mating pairs were classified as ‘successful’, while unmated flies were labeled as ‘unsuccessful’. Five morphometric traits were measured in a sample of 141 unsuccessful and 149 successful males: eye length (EL), head width (HW), thorax length (TL), face width (FW), and wing length (WL). An exploratory non-parametric Spearman’s rank correlation test indicated that mated males were in average larger for all traits (P < 0.01) except FW, indicating that with the exception of FW all traits are positively correlated with mating success. Step-wise multiple regression and principal component analysis logistic regression indicated that the most likely targets of selection were TL, EL, and FW. The two former are positively correlated, while FW is negatively correlated with the fitness component analyzed here (male mating success). In previous studies where male-male interaction had been removed experimentally, EL was shown to be associated with female choice and no effect relative to mating success was detected on TL. On the basis of that study and the present results it is tempting to suggest that body size (TL) might be important in intra-sexual selection. However, size was found to be strain dependent and flies from the wild were on average bigger than laboratory ones. Size selection might then be correlated with copulatory success, as a side effect due to selection of wild males over lab males due to differential sexual activity or other causes. The potential importance of both intra-sexual selection (male-male interactions) and inter-sexual selection (mate choice) on the morphology of Ceratitis capitata is discussed on the basis of the results presented here and previous works.

Size influences male mating success in the alfalfa blotch leafminer (Diptera: Agromyzidae)

Male size is an important parameter in mate choice for many species and has been associated with such female life-history parameters as increased fecundity or fertility and larger progeny (Phelan and Baker 1986; Savalli and Fox 1998, 1999; Brown 1999). In the alfalfa blotch leafminer, Agromyza frontella (Rondani), intraspecific larval competition may significantly influence the size of both males and females (Quiring and McNeil 1984a). The influence of female size on female reproductive success has been studied (Quiring and McNeil 1984b, 1984c), but to date, no attention has been given to the possible effects of male size. The objectives of this study were to determine if differences in male size, the result of intraspecific larval competition, affected male longevity and reproductive success, as well as various parameters of female reproduction.

The Effect of Male Size and Sex Ratio on the Duration of Precopulatory Mate Guarding in the Hermit Crab Pagurus filholi

The Effect of Male Size and Sex Ratio on the Duration of Precopulatory Mate Guarding in the Hermit Crab Pagurus filholi

Duration of paternal care in pine engraver beetles: why do larger males care less?

Male pine engravers, Ips pini (Coleoptera: Scolytidae), assist their mates during reproduction by removing the debris that accumulates while females excavate oviposition tunnels in the phloem tissue of host tree bark. Although duration of paternal care and male reproductive success are positively correlated, large males leave their mates and brood sooner than small males. We address two hypotheses to explain the earlier departure of larger males from their breeding galleries: (1) females oviposit most rapidly when paired with large males, thereby reducing the length of time that paternal care increases male reproductive success, (2) larger males have better prospects for future reproduction, and thus leave their galleries in search of new breeding opportunities sooner than smaller males. Contrary to the first hypothesis, when females were paired either with large or small males, there was no effect of male size on their rate of oviposition. Consistent with the second hypothesis, males that initiated breeding galleries were larger than males from the general population. In addition, large males flew farther and faster on flight mills than small males, which may indicate that large males have an advantage in locating suitable breeding sites. Thus, we suggest that large male pine engravers leave their galleries earlier than small males because large individuals have better prospects for future reproduction.