Small Males Research Articles

Foraging strategy as a route for sexual size dimorphism evolution.

Female-biased sexual size dimorphism stands as a widespread evolutionary pattern. Fecundity selection, favouring larger females with greater reproductive output, is a leading explanation. However, larger body sizes demand greater energy intake, potentially hindering the evolution of extreme female sizes. Thus, the evolution of more lucrative foraging tactics may allow for an increase in size. Hence, coupled with selection against larger males, fecundity selection should result in larger SSD in species with more lucrative foraging strategies. Crab spiders are sit-and-wait predators that hunt in several plant substrata. Species that forage on flowers or employ prey-luring strategies likely have access to higher food intake than other species. We extracted body size measurements of 614 crab spider species from 43 genera and classified them based on their foraging strategy. Our findings show that foraging strategies that provide higher energy input (EFS) result in larger SSD. Statistical estimates indicate that females have a cephalothorax width 91% larger than males in EFS species, compared to 26% larger females than males in non-EFS species. These differences possibly arise due to larger females and smaller males. The effects on male size reduction might result from scramble competition, whereas the increase in female size is likely due to fecundity selection. These results suggest that the shift towards more lucrative foraging strategies may have been a key event in body size and SSD evolution in crab spiders.

Effects of Nest‐Site Availability on Male–Male Competition and the Foraging Costs of Egg Attendance in an Arachnid With Exclusive Paternal Care

ABSTRACTNatural cavities are monopolizable resources used as nest sites across many species exhibiting exclusive male care. However, our understanding of how the availability of this type of reproductive site influences male–male competition and the foraging costs associated with parental care is limited and based on studies of fish. The harvestman Magnispina neptunus offers the opportunity to explore these questions in invertebrates because males defend natural cavities used as oviposition sites and provide exclusive parental care. We hypothesized that low nest availability would increase male–male competition and the foraging costs of egg attendance. To test this hypothesis, we collected observational data in the field and conducted a laboratory experiment with two groups, low and high nest availability. Field data indicate natural cavity scarcity, as only 50% of the males were nest holders. Larger males were more likely to hold nests in the field, but body size did not predict nest ownership in the laboratory. In the field, nests with openings smaller than average were equally occupied by small and large males, while nests with openings larger than average were occupied almost exclusively by large males. The nest opening in the laboratory experiment was adjusted to be equal to the average found in the field, which may have increased nest defensibility, regardless of male size. Thus, prior residency may outweigh body size in determining nest possession. Because nest owners seem to have an advantage over intruders, the costs of abandoning a nest are likely high. This may explain why the frequency of nest takeovers and foraging outside the nests did not differ between experimental groups. In conclusion, although underexplored in empirical studies, external factors, such as the opening size of cavities defended by males of many species with resource‐defense mating systems, may play a key role in the defensibility of nest sites.

Energetically costly weaponry in the large morph of male stag beetles

AbstractMales of many species develop disproportionately large weapons, and frequently the weapon size increases more quickly with body size in small than in large males—a trend often considered to result from the depletion of developmental resources limiting male weapon exaggeration. Based on the cost‐minimization hypothesis, a shallower weapon‐body size allometric slope in large than in small males could be selected for if the energetic maintenance costs of having oversized weapons increase faster in large than in small males. Whether males of different size groups that differ in the weapon‐body size allometric relationship also differ in the energetic costs of maintaining their weapons has not yet been investigated. Consequently, we studied this using the stag beetle (Cyclommatus mniszechi), in which males are larger in size and have larger mandibles than do females and are divided into two morphs: majors are larger and have longer mandibles than minors. In both male morphs, mandible size increases disproportionately with their body size, but it increases more quickly in minors than in majors. We measured the standard metabolic rate (SMR) of the three types of these beetles (the two male morphs and females) to investigate whether the energetic maintenance cost of carrying weapons differs among them. Body weight explained 80% of the variation in the SMR in the three types of beetles, and SMR increased more quickly with body weight in major males than in minor males or females. Weapon and body size also jointly explained approximately 80% of the variation in the SMR. Whereas SMR increased with body size in all three types of beetles (with a higher rate of increase in major males than in minor males or females), only the major males' SMR increased with weapon size. Overall, being heavier and larger and carrying oversized weapons are energetically costly in major males, something which could constrain the exaggeration of their weapons.

Morphometric variation and deteriorating food availability both explain seasonally declining reproductive success of Dicrurus hottentottus (Hair-crested Drongo)

Abstract Seasonally declining reproductive performance in avian populations may be attributed to high-quality individuals breeding earlier than low-quality individuals (the quality hypothesis), to deteriorating environmental conditions (the date hypothesis), or both. By comparing the reproductive performance among different perennial pairs, and the same perennial pairs across different years, we tested the influence of timing of breeding on reproductive performance in Dicrurus hottentottus (Hair-crested Drongo) from 2010 to 2022. Breeding pairs that typically laid earlier relative to the population mean (i.e., early-breeding pairs) exhibited a significantly higher fledging rate compared to breeding pairs that often bred later relative to the population mean (i.e., late-breeding pairs). For a given pair, the fledging rate of early-breeding pairs increased when they bred later compared to other years, while the fledging rates of late-breeding pairs were significantly lower in years when they bred later than usual. We found that male morphological traits were associated with both the timing of breeding and the feeding rate. Pairs with long-billed (indicator of high quality) males bred earlier than pairs with short-billed males, and pairs with larger males (indicator of high quality) had a higher feeding rate than pairs with smaller males. Female age had reversed effects on the timing of breeding and fledging rate: older females tended to breed earlier than younger females; but there was a sharp decline in fledging rate after 7 years of age in late-breeding pairs. Finally, our results showed that the feeding rate and the amount of invertebrate biomass decreased with laying date, indicating deteriorating feeding conditions later in the breeding season. Overall, our findings support both the quality hypothesis and the date hypothesis. Low-quality D. hottentottus are likely to be most adversely affected by the phenological mismatches induced by climate change, which, in turn, may affect population dynamics through reduced fecundity.

Adoption of satellite behavior by small male green treefrogs, Dryophytes cinereus, is not associated with age: Implications for the maintenance of alternative behavioral phenotypes

AbstractBody size is often a critical determinant of competitive ability and reproductive behavior. For example, small males characteristically lose contests with larger males and may be metabolically constrained from sustaining energetically demanding reproductive behaviors. Small males thus often utilize alternative reproductive tactics (ARTs) to maximize their reproductive success. How variation in body size among behavioral phenotypes arises can provide important insight into the maintenance of ARTs. For instance, smaller body sizes for males adopting ARTs may simply be a function of age, suggesting that the tactic is maintained by the periodic recruitment of young males into the population. Alternatively, body size differences among behavioral phenotypes that are unrelated to age suggest disparate growth rates that potentially arise as a consequence of variation in environmental conditions during development or genotypic differences between the phenotypes. Here we examine these alternative scenarios in the green treefrog, Dryophytes cinereus, using skeletochronological analysis combined with body size measures. As with many other anuran amphibians, male green treefrogs conditionally adopt a noncalling satellite mating tactic and attempt to intercept females attracted to the vocalizations of calling “host” males. We show that males adopting satellite behavior in natural choruses are smaller than calling males but do not represent a class of younger individuals, indicating that satellite males have lower growth rates than calling males. We also show that satellite males are in poorer condition than larger calling males, implicating energetic constraints in size‐related variation in mating tactic expression. Our work suggests that environmental conditions during development, genetic differences between phenotypes, or both, give rise to size discrepancies in behavioral phenotypes, neither of which have been previously explored in anurans. We discuss body size and condition differences between behavioral phenotypes in the context of energetic constraints and endocrine mediation of tactic expression in this species.

Voronoi diagrams and Delaunay triangulation for modelling animal territorial behaviour.

We explore the use of movable automata in numerical modelling of male competition for territory. We used territorial dragonflies as our biological inspiration for the model, assuming two types of competing males: (a) faster and larger males that adopt a face-off strategy and repulse other males; (b) slower and smaller males that adopt a non-aggressive strategy. The faster and larger males have higher noise intensity, leading to faster motion and longer conservation of motion direction. The velocity distributions resemble the Maxwell distributions of velocity, expected in Brownian dynamics, with two probable velocities and distribution widths for the two animal subpopulations. The fast animals' trajectories move between visually fixed density folds of the slower animal subpopulation. A correlation is found between individual velocity and individual area distribution, with smaller animals concentrated in a region of small velocities and areas. Attraction between animals results in a modification of the system behaviour, with larger animals spending more time being surrounded by smaller animals and being slowed down by their interaction with the surroundings. Overall, the study provides insights into the dynamics of animal competition for territory and the impact of attraction between animals.

Squid male alternative reproductive tactics are determined by birth date.

Alternative reproductive tactics (ARTs) are discontinuous phenotypes associated with reproduction, observed in males of many species. Typically, large males adopt a tactic of competing with rivals for mating, while small males adopt a tactic of stealing fertilization opportunities from the large males. The 'birth date hypothesis', proposing that the date of birth influences the determination of each male's reproductive tactic, has been tested only in teleost fish to date. Here, the birth date hypothesis was tested in ARTs of Japanese spear squid Heterololigo bleekeri (consort/sneaker) by analysing statolith growth increments. The birth date significantly differed between consorts (early-hatched) and sneakers (late-hatched). However, no differences were detected in growth history up to 100 days from hatching. Most immature males caught during the reproductive season were larger than sneakers, and their hatch date was similar to that of consorts, suggesting that these immature males had already been following a life-history pathway as a consort. These results indicate that ARTs of H. bleekeri are determined based on their hatch date in early life. This study firstly suggests that the birth date hypothesis applies to aquatic invertebrates, suggesting that the mechanism by which birth date determines the individual phenotype is a phenomenon more common than previously believed.

Size structure, age, and growth of the blue shark, Prionace glauca (Linnaeus, 1758) in southern Brazil.

The blue shark is a highly migratory species with a worldwide distribution, making it susceptible to multiple fishing fleets across the globe. In southern Brazil, it is an important target, comprising up to 40% of the total biomass landed by the commercial surface longline fleet. This study aims to contribute to a better understanding of how the species uses the region and to update its life-history information available for future assessments. Over five consecutive years (2018-2022) of landings and onboard monitoring, we gathered size data and vertebral samples to describe the species size composition in the region, as well as its seasonal and interannual variability and to update estimated life-history parameters. The results showed that southern Brazil is mainly inhabited by large juvenile males that arrive during winter (July-September) and stay until spring (October-December), when their frequency decreases. Small adult males are present throughout the year but in higher frequencies during summer. A small number of adult females are present with higher frequencies during spring and summer, which decreases during the austral autumn and winter. Some variability in the presence of each life stage was observed among years. The estimated life-history parameters were as follows: L∞: 255.02 cm fork length (FL), k: 0.20, L0:35.68 cm FL for males; L∞: 246.47 cm FL, k: 0.23, L0:36.77 cm FL for females; and L∞: 269.58 cm FL, k: 0.18, L0:36.19 cm FL for pooled sexes. However, the estimated values must be cautiously interpreted, as the obtained samples cannot be construed as representative of the entire harvested stock due to the lack of consistent presence of some life stages in the study region.

Small-bodied males invest in larger testes when highly ornamented.

Sperm competition and male mating rate are two non-mutually exclusive key evolutionary pressures selecting for larger testes within and across animal taxa. A few studies have tried to test the role of mating rate in the absence of sperm competition. Under the mating rate hypothesis, particular phenotypes of a given population that are expected to gain more mates (e.g., more ornamented males) are expected to make higher investments in testes size (a proxy for sperm production). We test this prediction in Polistes simillimus, a neotropical paper wasp in which females are single mated (no sperm competition) and males can mate with multiple partners. Testes size was predicted by body size (positive association), sexual ornamentation (negative association), and their interaction (among small males, testes size was positively related to ornamentation, but the opposite pattern was observed among large males). We propose that small-bodied well-ornamented males may face the highest risk of sperm depletion. Small-bodied males make relatively higher investment in testes size when highly ornamented. This strategy might be less profitable to large males, as they have overall larger testes. Our results provide strong evidence for the mating rate hypothesis.

Diet and body size modulate the remating behaviour of a predaceous ladybird, Coccinella transversalis (Fabricius) (Coleoptera, Coccinellidae)

The nutritional condition and body size influence the mating and female remating behaviour of a predaceous ladybird, Coccinella transversalis. When well-fed males were provided with females of three different dietary conditions, viz. (i) well-fed, (ii) food-deprived and (iii) honey-fed, the well-fed ones were most fecund with highest percentage of egg-viability and least preoviposition period and remating refusals, while food-deprived ones showed vice-versa. However, honey-fed females laid unfertile eggs after coercively mating with males, and resisted the most to remate, which gets strengthened in the second mating trial. This indicates females’ nutritional condition modulates the females’ mating behaviour and post-mating outcomes. The adult body size was directly proportional to reproductive output with heavier females showing high fecundity and percentage of egg viability with least preoviposition period than the lighter ones. Large females resisted the least to remate with larger males than with smaller males, while large males coercively mated with smaller females. Regardless of body-size, the females’ remating resistance was enhanced in the second mating trial. Both diet and adult body size modulate the re-mating behaviour of female C. transversalis, as the food-deprived and large females greatly resisted to re-mate with smaller males.

Tanytarsus deimos group (Chironomidae, Diptera) for two distinctive species from the Neotropics

Two species of the genus Tanytarsus van der Wulp, 1874 are described: T. deimos Giłka, Dantas et Andersen, sp. nov. (Mexico, Panama) and T. phobos Dantas, Giłka et Andersen, sp. nov. (Peru). Small adult males having wings with a high venarum ratio, unpaired tibial spurs on mid and hind legs, a hypopygial anal point lanceolate without spinulae or bars, a digitus with a well-developed basal tubercle bearing a long seta, a stout median volsella, and a gonostylus distinctly shorter than the gonocoxite, are a set of characters common to the two close species for which a new group is here proposed.

Weapon allometry and shape variation in the Helm’s stag beetle (Geodorcus helmsi)

Abstract Many animals develop and use exaggerated weapons in contests over access to mating opportunities. Stag beetles (family Lucanidae) show striking sexual dimorphism, where the males have heavily exaggerated mandibles that the females do not possess. In some genera, size and shape can also vary drastically between small and large males resulting in discrete alternative male morphs, described as male dimorphism. The genus Geodorcus is a poorly studied and threatened group of stag beetles that are endemic to New Zealand. Geodorcus helmsi is the most widespread species in this genus and presents an opportunity to test for the presence of both sexual and male dimorphism and investigate the scaling relationships (allometry) of mandibles in this group. We used linear and geometric morphometric analyses on wild populations and museum specimens from Stewart Island, New Zealand, to assess whether G. helmsi exhibits male dimorphism. We found that within a single population, there is no evidence for alternative male morphs, but a gradual shift between smaller and larger individuals. We also found that male mandibles exhibit steep positive allometry in contrast to the negative allometry found in the mandibles of females, as is often found for sexually selected weaponry. Moreover, we found evidence that left and right mandibles of G. helmsi are subtly asymmetric. Our results provide context for the competitive behaviour observed in this species, and give insights into potential trade-offs between smaller and larger individuals of the Helm’s stag beetle.

Male reproductive output and sperm competition as indicated by gonadosomatic index in Paddlefish stocks

AbstractObjectiveWe investigated if large Paddlefish Polyodon spathula invest in testis weight disproportionately more than smaller males, as expressed by the gonadosomatic index (GSI). The approach was to assess the relation between testis weight F (i.e., the combined weight of both testes) and fish weight W in the expression F = aWb. The hypothesis was that sperm competition in Paddlefish would be expected (with b > 1) based on observations of several male fish attending a female spawner in a past study in the Osage River, Missouri.MethodsWe used a large, three‐state data set from three fisheries (Montana, North Dakota, and Oklahoma) to evaluate isometry and allometry in the power function relationship between fish weight and testis weight.ResultAll three data sets showed hyperallometric increases in testis weight with fish weight (i.e., b > 1). For Montana males, hyperallometry was greatest (b = 1.56; n = 8798), followed by North Dakota (b = 1.36; n = 8209) and Oklahoma (b = 1.22; n = 9571). Paddlefish from Montana and North Dakota had much lower testis weights through age 18 and much lower fish weights through age 25 than Oklahoma Paddlefish. By ages 17–25, mean male GSI in Oklahoma declined, whereas it remained level at about 1.5 for combined Montana and North Dakota Paddlefish. Throughout their lives, at each age, Montana and North Dakota Paddlefish allocated a higher percentage of their total weight to testis weight and reached a higher asymptotic GSI (GSI∞) than did Oklahoma Paddlefish; GSI∞ was 1.50 for Montana fish, 1.44 for North Dakota fish, and 1.26 for Oklahoma fish.ConclusionResults provide evidence supporting the occurrence sperm competition (i.e., b > 1), as would occur when two or more males compete to fertilize the eggs of a female spawning Paddlefish. Comparisons among species and stocks are made but were limited by an acute shortage of data on male testis weights and other testis characteristics (e.g., sperm size, energy content), and reproductive investment in Paddlefish and most other fishes in other localities.

Behavioral estimates of mating success corroborate genetic evidence for pre-copulatory selection

Abstract In promiscuous species, fitness estimates obtained from genetic parentage may often reflect both pre- and post-copulatory components of sexual selection. Directly observing copulations can help isolate the role of pre-copulatory selection, but such behavioral data are difficult to obtain in the wild and may also overlook post-copulatory factors that alter the relationship between mating success and reproductive success. To overcome these limitations, we combined genetic parentage analysis with behavioral estimates of size-specific mating in a wild population of brown anole lizards (Anolis sagrei). Males of this species are twice as large as females and multiple mating among females is common, suggesting the scope for both pre- and post-copulatory processes to shape sexual selection on male body size. Our genetic estimates of reproductive success revealed strong positive directional selection for male size, which was also strongly associated with the number of mates inferred from parentage. In contrast, a male’s size was not associated with the fecundity of his mates or his competitive fertilization success. By simultaneously tracking copulations in the wild via the transfer of colored powder to females by males from different size quartiles, we independently confirmed that large males were more likely to mate than small males. We conclude that body size is primarily under pre-copulatory sexual selection in brown anoles, and that post-copulatory processes do not substantially alter the strength of this selection. Our study also illustrates the utility of combining both behavioral and genetic methods to estimate mating success to disentangle pre- and post-copulatory processes in promiscuous species.

Sexually attractive traits predict predation-threat sensitivity of male alternative mating tactics

Abstract Although visual sexual signals, such as ornamental colors and courtship displays, and large body size in males are attractive to females in numerous species, they may also inadvertently attract the attention of eavesdropping predators and thus may be costly in terms of increasing individual risk of mortality to predation. Theoretically, more color ornamented and larger males should be more predation threat sensitive and suppress their sexual signaling and(or) mating effort relatively more than their less color ornamented and smaller counterparts when under predation hazard. Here, we experimentally tested this hypothesis by quantifying concurrently the rates of alternative mating tactics (courtship displays, sneak mating attempts) expressed by male Trinidadian guppies (Poecilia reticulata) varying in color ornamentation and body size under a staged immediate threat of predation. Males suppressed their overall mating effort in response to the perceived predation threat, decreasing the frequency of their (presumably more conspicuous) courtship displays significantly more on average than the frequency of their sneak mating behavior. Statistically controlling for body length, more color-ornamented males were more threat sensitive in their courtship displays, but not sneak mating attempts, under predation hazard than drabber males. Controlling for body coloration, larger males exhibited lower courtship and sneak mating efforts than smaller males in both predation treatments, but body length only influenced threat sensitivity in sneak mating behavior. These results are consistent with both the threat sensitive hypothesis and asset protection principle and highlight the phenotype dependency and adaptive plasticity of alternative mating tactics in male guppies under varying predation risk.

Rates of male rivalry and mate choice vary with density and determine whether size-assortative mating is absent, positive, or negative in the clown weevil, Eudiagogus pulcher

At four sites in Texas, the density of the clown weevil, Eudiagogus pulcher, in stands of rattlebox, Sesbania drummondii, increased with proximity to water. Size-assortative mating (SAM) was negative at high density, positive at intermediate density, and absent at low density. Only at intermediate density were relatively small potential mates frequently rejected. Females rejected males via resistance to attempts to mount while males rejected females by abandoning them soon after mounting. A laboratory experiment showed that mate rejection is more likely when individuals experience intermediate densities, but not low or high densities, prior to courtship. In the field, rival males displaced mounting males that were small relative to either the female or rival. Rates of rivalry increased with density. At high density, low rates of mate rejection and high rates of rivalry resulted in the formation of displacement-resistant pairs consisting of large males and small females. This left small males to vie for large females and resulted in negative SAM. At intermediate density, low rates of rivalry coupled with rejection of small individuals favored the formation of pairs consisting of similarly sized males and females, causing positive SAM. At low density, low rates of both mate rejection and rivalry resulted in random mating by size and the absence of SAM.

Distribution pattern and habitat use of the protandrous shrimp Pandalus latirostris in relation to environmental characteristics in Akkeshi waters on the pacific coast of eastern Hokkaido, Japan

A sampling of the protandric shrimp, Pandalus latirostris, was conducted at fixed sites from July 2015 to March 2020 in Akkeshi Bay and the connecting Lake Akkeshi on the Pacific coast of eastern Hokkaido. Based on the occurrence pattern of P. latirostris, most individuals begin mating as males at Age-1, followed by a sex change to females, spawn eggs as females at Age-2, and hatch their eggs in the spring of Age-3. Pre-hatching ovigerous females were mainly found in eelgrass beds near and in Lake Akkeshi, where the water temperature was relatively high. The females probably migrate there to hatch their eggs, making sure of the high survival and growth of the hatched larvae. Juveniles and small males were also abundant in near and in Lake Akkeshi, indicating that many larvae remained in the eelgrass beds where they hatched. These eelgrass beds play an important role in the maintenance of the shrimp population as a major egg-hatching site and nursery habitat in Akkeshi waters. With ontogenetic development, the occurrence rate of P. latirostris gradually increased on the offshore side of Akkeshi Bay, with its body size being larger. As P. latirostris grow, they will probably disperse to the offshore side of Akkeshi Bay. However, the density of P. latirostris in the eelgrass bed in the bay near the lake was extremely high, with its strong preference at all ontogenetic stages. This eelgrass bed would help maintain the shrimp population as a “key habitat” for the shrimp. The site-specific environmental characteristics of vegetation beds influence the distribution and abundance of individuals within a population of P. latirostris through their growth and the associated change in habitat preference. In this study, the importance of maintaining the diverse habitats of P. latirostris will be discussed as part of the shrimp stock management measures.

Male size does not affect the strength of male mate choice for high-quality females in Drosophila melanogaster.

Theory predicts that the strength of male mate choice should vary depending on male quality when higher-quality males receive greater fitness benefits from being choosy. This pattern extends to differences in male body size, with larger males often having stronger pre- and post-copulatory preferences than smaller males. We sought to determine whether large males and small males differ in the strength (or direction) of their preference for large, high-fecundity females using the fruit fly, Drosophila melanogaster. We measured male courtship preferences and mating duration to show that male body size had no impact on the strength of male mate choice; all males, regardless of their size, had equally strong preferences for large females. To understand the selective pressures shaping male mate choice in males of different sizes, we also measured the fitness benefits associated with preferring large females for both large and small males. Male body size did not affect the benefits that males received: large and small males were equally successful at mating with large females, received the same direct fitness benefits from mating with large females, and showed similar competitive fertilization success with large females. These findings provide insight into why the strength of male mate choice was not affected by male body size in this system. Our study highlights the importance of evaluating the benefits and costs of male mate choice across multiple males to predict when differences in male mate choice should occur.

Reproductive benefits and reduced investment in parental care behavior associated with reproductive groups of males in Abudefduf troschelii.

Fishes of the family Pomacentridae present a wide diversity of mating systems, ranging from polygyny to promiscuity and from individual territorial defense to the establishment of reproductive colonies of males. The damselfish species Abudefduf troschelii has a reproductive colony mating system, in which males temporarily aggregate in reproductive areas to court and attract females. Males defend an individual territory where they receive eggs and perform paternal care behaviors for their offspring. The present study evaluated the advantages of the colonial mating system in A. troschelii. During an entire reproductive period, in a breeding colony within a rocky reef, we located, marked, geo-referenced, and measured the distances between the territories of all males. We quantified the variance among males in their patterns of paternal care investment, eggs acquired, hatching success, reproductive success, body size, and changes in body coloration. We found that males spatially distributed their nests in groups or independently (i.e., solitary nests). Nesting groups are formed by larger males that show intense nuptial coloration during the entire receptivity period. They are located centrally to the colony and consist of three to six males whose territories overlap. In contrast, small solitary males that fail to acquire or maintain nuptial coloration during the receptivity period establish their nests peripherally to the colony, away from the territories of other males. Our results highlight that the reproductive benefits of colonial nesting are unequal for males, as the spatial distribution of nests within the colony determines the reproductive success of males. Group nesting confers the highest reproductive benefits to males regarding eggs obtained, hatching success, and relative fitness and also enables males to reduce their parental investment in brood care behaviors. The preference of females for oviposition could be associated with greater intrasexual competitiveness, defense ability, body condition, or experience of group-nesting males located at the center of the colony or because their progeny will have a lower probability of predation than they would in solitary nests males.

Sexual maturation and allometry of reproductive traits in large- and small-sized male honeybees

The body size of male honeybees (Apis mellifera L.) is a cause of skewed reproductive success. Large males are usually produced in colonies and have advantages in competition for mating and fertilisation. However, distinct small-sized males were produced depending on the colony conditions, particularly under queen-less conditions. Understanding the reproductive traits of small-sized males is currently limited, but it may provide insight into the developmental patterns and reproductive strategies that maximise reproductive success depending on body size and colony conditions. This study evaluated the process of sexual maturation in large- and small-sized males and the allometry between reproductive traits and body size. Changes in reproductive traits, including reproductive organs, number of spermatozoa, and sperm density, occurred earlier in small-sized males than in large-sized males after emergence. These results suggest that small males are precocious. The relatively early development of small-sized males would reflect the low developmental cost, which is likely to allow the production of many males and ensure reproductive success under circumstances in which available resources are limited. Furthermore, reproductive traits were positively correlated with body size, but allometry was different for these traits. Hence, the findings suggest that there is a given investment pattern toward reproductive traits with increasing body size, which would be responsible for high mating and fertilisation success in large males.