Large Territorial Males Research Articles

Conditional alternative movement tactics in male crocodiles

In species where conflict is costly, individuals adopt alternative movement tactics to minimise the risk of competitive interactions. Dominant males often maintain defined territories, while less competitive males may be forced to adopt alternative tactics to maximise fitness and reduce conflict. However, the extent to which males switch tactics according to current social or physiological status is poorly understood. Using implanted acoustic tags and a fixed array of tracking receivers, we investigated how the behaviour of 78 male estuarine crocodiles (Crocodylus porosus) shifted over an 11-year period in relation to ontogeny, body condition, and the extent of physical injuries. We discovered that male crocodiles sorted into three common movement classes, with 51% of males maintaining the same movement class across consecutive years (max = 9 years). Males > 4 m in total length maintained confined territories both within and across years and had the greatest extent of injuries and the highest condition score, indicative of territory holders. In contrast, smaller males sorted into high movement roamer or low movement site-philopatric tactics, where the tactic an individual adopted was less stable between years and did not correlate with condition or external injuries. Our study reveals the socio-biological mechanisms by which estuarine crocodiles coexist within a restricted habitat.Significance statementIdentifying individual-level differences in movement helps us predict which individuals are more likely to be involved in human-wildlife interactions. However, studying long-term shifts in movement is challenging, as large datasets of co-occurring individuals tracked in their natural environment over multiple years are required. We tracked a population of 78 male estuarine crocodiles (1030–4687 mm total length) in a shared environment over 11 years and assessed how eight movement traits were linked to body size and physical condition. At the population level, males sorted into different movement tactics according to ontogeny, with large territorial males having better body condition yet a greater incidence of injury. However, 49% of males showed variability across years, suggesting that tactics were conditional relative to environmental variability and a male’s own status. Our study provides insights into the mechanisms and costs of movement tactics in wild crocodile populations.

Bachelor groups form due to individual choices or environmental disrupters in African striped mice

In several mammal species, bachelor groups occur as a regular life history stage between dispersal and becoming the breeding male of a multifemale group. How such groups come into existence and how males that choose this strategy differ in life history traits from other males is rarely investigated. Males of the socially flexible African striped mouse, Rhabdomys pumilio , have been historically reported to adopt one of three alternative tactics: small group-living philopatric males, intermediate solitary roaming males or large group-living territorial males. Here, we describe for the first time, bachelors as a fourth male tactic. A long-term study on 13 generations of striped mice revealed two types of bachelor groups: (1) kin bachelor groups formed when all females disappeared, probably due to predation, and (2) nonkin bachelor groups formed by unrelated males that originated from different groups. Whereas kin bachelor groups occurred more frequently during the nonbreeding season, nonkin bachelor groups were most common in the breeding season and had a shorter tenure, since most of these males soon switched to the solitary roaming tactic or the territorial breeder tactic. Importantly, we found that nonkin bachelors were heavier and older than kin bachelors and that they did not differ from solitary roaming males in body mass and age. We therefore identified two different forms of bachelor groups, small kin bachelors whose female group members disappeared and larger nonkin bachelor groups showing traits of an alternative reproductive tactic. Both types of bachelor groups differed in multiple traits, demonstrating that it is important to follow the life histories of individuals to understand the mechanisms leading to alternative tactics. • We describe bachelor groups as a fourth male tactic in striped mice. • Kin bachelor groups form when all females disappear. • Nonkin bachelor groups are formed by unrelated males from different groups. • Both types of groups differ in body mass, age and seasonality of occurrence.

Territorial Males Can Sire More Offspring in Nests with Smaller Doors in the Cichlid Lamprologus lemairii

To examine how territorial males counter reproductive parasites, we examined the paternity of broods guarded by territorial males using 5 microsatellite loci and factors that determine siring success in a wild population of the Lake Tanganyika cichlid Lamprologus lemairii. Females enter rock holes (nests) and spawn inside, and territorial males release milt over the nest openings. Sneakers attempt to dart into the nests, but territorial males often interrupt the attempt. The body size of territorial males (territorial defense ability) and the size of nest opening (the ability to prevent sneakers from nest intrusions) are predicted to be factors that affect paternity at the premating stage, whereas milt quality traits are factors that affect paternity at the postmating stage. Parentage analyses of 477 offspring revealed that most clutches have few or no cuckolders, and territorial males sired >80% of eggs in 7 of the 10 analyzed clutches. Larger territorial males that spawned in nests with narrower openings had greater siring success. In contrast, none of the milt traits affected the siring success. These suggest that territorial male L. lemairii adopt premating strategies whereby they effectively prevent reproductive parasitism.

Body size correlates with fertilization success but not gonad size in grass goby territorial males.

In fish species with alternative male mating tactics, sperm competition typically occurs when small males that are unsuccessful in direct contests steal fertilization opportunities from large dominant males. In the grass goby Zosterisessor ophiocephalus, large territorial males defend and court females from nest sites, while small sneaker males obtain matings by sneaking into nests. Parentage assignment of 688 eggs from 8 different nests sampled in the 2003–2004 breeding season revealed a high level of sperm competition. Fertilization success of territorial males was very high but in all nests sneakers also contributed to the progeny. In territorial males, fertilization success correlated positively with male body size. Gonadal investment was explored in a sample of 126 grass gobies collected during the period 1995–1996 in the same area (61 territorial males and 65 sneakers). Correlation between body weight and testis weight was positive and significant for sneaker males, while correlation was virtually equal to zero in territorial males. That body size in territorial males is correlated with fertilization success but not gonad size suggests that males allocate much more energy into growth and relatively little into sperm production once the needed size to become territorial is attained. The increased paternity of larger territorial males might be due to a more effective defense of the nest in comparison with smaller territorial males.

Sex recognition of female-like sneaker males in the Comanche Springs pupfish, Cyprinodon elegans

In mating systems with alternative reproductive tactics, female mimicry may allow some males to avoid aggression from larger territorial males and garner matings. However, selection is predicted to favour the territorial males' ability to discriminate against female mimics as they may usurp fertilizations in a male's territory and potentially eat eggs fertilized by the territory owner. I tested whether territorial males were able to recognize female-like sneaker males in the natural population of Comanche Springs pupfish, Cyprinodon elegans . Results of a field study conducted at Balmorhea State Park, Balmorhea, TX, U.S.A., revealed that territorial males behaviourally discriminate size and sex of conspecifics. They were more aggressive to large males than to sneaker males. However, territorial males also directed more aggressive behaviours towards sneaker males than similarly sized females. As sneaker males garner little aggression when a large male intruder is also present, they will potentially gain opportunities to spawn if large males commonly intrude into males' territories. These results suggest that aggression towards sneaker males is context dependent and that the social environment may have important evolutionary fitness consequences for both territorial males and sneaker males. ► Female mimics deceive territorial males to garner matings. ► Territorial male Cyprinodon elegans identify female-like sneakers as males. ► Aggression towards sneaker males is context dependent. ► Population demographics may determine the successfulness of sneaker males.

Adoption and cuckoldry lead to alloparental care in the tessellated darter (Etheostoma olmstedi), a non-group-living species with no evidence of nest site limitation

While extensive empirical and theoretical work has focused on the evolution of costly cooperation (particularly in group-living species), less attention has been paid to more low-risk or immediately beneficial forms of cooperation. In some non-group-living darters, alloparental care (or allocare) by subordinates has been noted to result from by-product benefits as small territorial (subordinate) males adopt and provide care to the abandoned eggs of large territorial (dominant) males. In the tessellated darter (Etheostoma olmstedi), allocare also results from sneak fertilization. However, information on the rate of allocare by tessellated darters is contradictory: prior behavioral work suggested that it is very common, while a genetic examination showed males to primarily care for their own young. We found behavioral and genetic evidence of very high levels of allocare at our study location. The relative size of the assigned fathers of young to the alloparental male is consistent with the idea that initial allocare primarily results from sneak fertilization (“cuckoldry-based allocare”), but later allocare results from subordinate males caring at previously abandoned nests (“adoption-based allocare”). Larger males appeared to breed more frequently at different nests, but did not father more individual offspring than smaller males. Finally, low relatedness between abandoning and alloparenting males suggests that kin selection does not contribute to alloparental care. We discuss how variation in nest availability may explain the inconsistent findings of the rate of alloparental care in the tessellated darter, and how increased research in this and similar systems can expand our understanding of the evolution of cooperation.

Social status-dependent nest choice of territorial males under reproductive parasitism in a Lake Tanganyika cichlid Telmatochromis vittatus

Field and laboratory studies were conducted to examine how territorial males of a Lake Tanganyika cichlid Telmatochromis vittatus balance the conflicting demands on nest choice between occupying large nests with more females and avoiding reproductive parasitism (nest piracy, which is adopted by the largest males in the population). Pirates less frequently intruded the nests farther from neighbours, perhaps due to the costs associated with travelling between nests. The field experiment showed that territorial male T. vittatus sacrificed the fitness benefits that large nests offer and instead prioritized occupying the nests farther from neighbours on which fewer pirates intruded. The field observations suggested that they adopt different strategies for nest choice according to their relative competitive ability to pirates; the large territorial males, who are size-matched to pirates and can defend their nests against them, compete for larger nests among the more-isolated nests, whereas subordinate territorial males, which are smaller than pirates and thus inferior to them, compete for the more-isolated nests among the less-isolated nests. These findings suggest that the territorial male T. vittatus chooses the more-isolated nests to avoid pirate males at the expense of occupying large nests.

Sperm phenotypic plasticity in a cichlid: a territorial male's counterstrategy to spawning takeover

Studies of sperm competition in species with alternative reproductive tactics (ARTs) often pay attention to the differences in investments in sperm between sneakers facing a higher sperm competition risk and bourgeois males facing a lower risk. Here, we examined within-tactic as well as among-tactic variations in sperm investments in the Lake Tanganyika shell-brooding cichlid Telmatochromis vittatus, a species with 2 types of parasitic tactics. Territorial male T. vittatus suffer reproductive parasitism by both smaller sneaker males and larger pirate males (‘‘pirates’’ take over the spawning event during which territorial males perform sneaking as a counterstrategy). We hypothesized that both territorial males living under the risk of pirates and sneakers face increased risk of sperm competition and therefore should produce high-quality sperm compared with both territorial males that experienced no piracy risk and pirates. As expected, field studies showed that the former 2 males produced longer lived sperm than the other males. Aquarium experiments demonstrated that a visual stimulus of a pirate was enough to induce an increase in sperm longevity in territorial males compared with when no such stimulus was given. These results indicate that territorial male T. vittatus can plastically adjust at least one sperm quality trait in response to piracy risk. Moreover, long-term monitoring of males in the field showed that small territorial males grow into large territorial males and finally into pirates, so ARTs are not fixed over life. Accordingly, male T. vittatus appear to ontogenetically change their sperm longevity in response to size-dependent sperm

Body temperature and body size affect flight performance in a damselfly

Flight performance is undoubtedly an important factor for behavioral success in flying insects. Though it is well-known that the flight performance is influenced by body temperature and body size, the relative importance of these factors is not well-understood. We performed laboratory experiments using the male-polymorphic damselfly Mnais costalis with larger territorial males and smaller non-territorial males in a population. We analyzed the effects of body temperature and body size, measured as the thoracic temperature and left hind-wing length, respectively, on two indices of flight performance: maximum lifting force and size-corrected lifting force. The latter is an index of acceleration that is related to aerial agility. The results showed that higher body temperature produced both larger maximum lifting force and larger size-corrected lifting force. In contrast, while larger size produced a larger maximum lifting force, it produced a lower size-corrected lifting force. The results of field measurements showed that territorial males had variable thoracic temperatures depending on the insolation in their territories. In contrast, non-territorial males had less variable and generally higher thoracic temperatures than territorial males as they are mostly found in sunny spots. Until now, the influence of body temperature on behavioral performance has remained unclear although considerable studies have suggested such influence. We showed, here, for the first time, combined effects of body size and body temperature on flight performance. We also showed that body temperature was influenced by the mating strategies of a damselfly. These findings provide new insights into the cost and benefits of territorial behavior in ectothermic animals.

Alternative mating tactics in the New Zealand fur seal (Arctocephalus forsteri): when non-territorial males are successful too

In polygynous mammals, the status of many males does not allow them to have a high social rank and theory predicts selection for alternative mating tactics. Alternative tactics were suggested to explain discrepancies between mating and paternity successes in several pinniped species. However, information on alternative tactics in fur seals is limited. Here, we focus on the polygynous New Zealand fur seal, Arctocephalus forsteri, predicting that competition for females is likely to cause a diversification of male mating tactics and that non-territorial tactics can yield reproductive success. We describe the behaviour of 38 males in a medium to large colony. Paternity success was assessed using CERVUS and PASOS, from a pool of 82 pups sampled at the study site and at neighbouring breeding areas. To see whether size is correlated with mating tactic, the length of 17 males was estimated using photogrammetry. Cluster analysis identified three male behavioural profiles: one corresponding to large territorial males and two illustrating alternative tactics employed by smaller non-territorial males. Of the 13 pups born at the study site that were assigned a father, eight were sired by three territorial males and five were sired by non-territorial males. Our study highlights that holding a territory is not a necessary condition for reproductive success in all otariids.

Sexual size dimorphism in the American rubyspot: male body size predicts male competition and mating success

Sexual differences in body size are widespread among animals, and various explanations for the evolution and maintenance of sexual size dimorphism have been proposed. We investigated the effects of sexual selection and fecundity selection on the sizes of males and females, respectively, in American rubyspots, Hetaerina americana. Males are larger than females and have large red spots at the base of each wing that are sexually selected via male-male contests. Mating success is determined by the ownership of a territory. Large males held territories for longer and sustained longer territorial fights than small males. Territorial males obtained more copulations than nonterritorial ones. Large males also had more wing pigmentation and mated with large females. Large territorial males had high energy reserves, whereas nonterritorial males appeared to have depleted reserves. Selection analyses of body size showed disruptive selection acting on male body size, suggesting that both small and large males may be favoured in terms of mating success. We also tested whether fecundity selection acts on female size. However, female body size was unrelated to the number of eggs carried. Taken together, our results suggest that in this territorial damselfly species male-biased size dimorphism is driven by large male size in male-male competition being selectively advantageous in territory acquisition and/or maintenance. We also suggest that small size is advantageous in nonterritorial males to improve their agility in courting (or subduing) females.

Social control of terminal phase transition in primary males of the diandric wrasse, Halichoeres poecilopterus (Pisces: Labridae)

In many diandric fishes, large territorial males with bright body coloration (terminal phase (TP) males) are derived either from initial phase (IP) females that change sex to male or from IP primary males that change color and behavior, but do not change sex. The mechanism controlling the transition of IP primary males into TP males is not well understood. We conducted cohabitation experiments to examine social conditions favoring TP transition by primary males in the diandric wrasse, Halichoeres poecilopterus. IP primary males always started TP-specific sexual behavior in the presence of a smaller subordinate, and subsequently acquired TP body coloration. In contrast, primary males under subordinate conditions often performed female-like sexual behavior. In pairs with similar body sizes, both individuals initiated TP male behavior. The results suggest that TP transition in primary males may be closely related to a dominance relationship (or size order) within social groups, as it is in the case of sex change by females.

Behavioral syndromes influence mating systems: floater pairs of a lizard have heavier offspring

Variation in correlated behaviors or behavioral syndromes could have interesting effects on mating systems, especially if the variation in syndrome exists in both sexes. Both males and females of the lizard Eulamprus heatwolei display two behavioral types of a behavioral syndrome, defined by correlations between territorial, exploratory, and predator avoidance behaviors. We tested how this variation in behavioral syndrome influences reproductive success, pairing patterns, and offspring weight. We used spatial behavior and residency in the field to identify territorial and floater individuals. Females were relocated to the laboratory to give birth, and all offspring, dams, and potential sires were genotyped to determine offspring paternity. During field surveys, 164 lizards were caught of which 27.5% were territorial and the rest were floaters. Paternity was assigned to 66% of the 104 offspring produced by 33 dams. Territorial sires fathered a greater proportion of the offspring of territorial dams than floater sires. Larger territorial males were more likely to sire the entire clutch or share paternity with fewer additional sires than smaller territorial males. Floater sire size, however, did not influence the number of fathers per litter. Floater females produced heavier offspring than their territorial counterparts, and offspring fathered by floaters were heavier than maternal half-sibs fathered by territorial males. We speculate that differences in offspring weight may be the result of differences in yolk provisioning by females and parent genetic compatibility. Key words: Eulamprus heatwolei, multiple paternity, offspring quality, personalities. [Behav Ecol]

Pre-copulatory ejaculation solves time constraints during copulations in marine iguanas

When animals compete for copulations, large body size often implies high mating success. Small males may, however, compensate for their competitive disadvantage by special adaptive traits. This is the case in marine iguanas, iguanid reptiles of the Galapagos archipelago. In marine iguanas, females copulate only once per season. During copulations, males needed 2.8—3.1 min to initiate ejaculation. Large territorial males copulated long enough (more than 3.1 min) to achieve ejaculations in 95% of copulations, even when disturbed. Small males were separated from females by rival males in 29% of copulations before the start of ejaculation. Small males nevertheless fertilized females using prepared viable ejaculate, which was kept in readiness in hemipenis pouches and transferred into the female cloaca at intromission. This tactic increased the mating success of small males by 41 %. This tactic demonstrates the adaptive significance of a trait which is functionally equivalent to non-ejaculatory ‘masturbation’, and appears to be unique for vertebrates. However, similar phenomena have occasionally been observed, but mostly lacked functional explanation. An ‘ejaculation-in-advance’ could occur in many taxa in which there is size-dominance hierarchy and sexual interference, but this remains to be determined.

Using Growth-Based Models to Study Behavioral Factors Affecting Sexual Size Dimorphism

In animals with asymptotic growth after maturity, a variety of factors can lead to inter- and intraspecific variation in sexual size dimorphism (SSD). Growth-based models tailored for a particular taxon provide a useful framework for analyzing questions about the proximate bases, adaptive significance, and evolution of SSD. This paper shows how growth-based models designed for Anolis lizards have been used to study the effects of male territorial and competitive behavior on SSD and adult size distributions. In a comparative study of different species of anoles, indices of SSD based on male and female asymptotic snout-vent length (SVL) have been used to confirm a prediction from territorial theory that SSD should be related to inter-female distance. Within populations of Anolis sagrei and Anolis limifrons, adult size distributions were sometimes skewed in favor of larger males than predicted by null growth-based models, as a result of the underrepresentation of small, young males in samples containing females of the same age. A relative shortage of newly mature males in adult size distributions is consistent with behavioral studies suggesting that young, small males may bear the brunt of aggression from larger territorial males. Hence, growth-based models can be used to suggest and test behavioral and other hypotheses about the factors affecting SSD.

The Influence of Population Density on the Mating System of Thalassoma pavo, a Protogynous Mediterranean Labrid Fish

Abstract. The aim of the present study is to determine the factor balancing the reproductive polymorphism obSérved in Thalassoma pavo, a Méditerranean labrid fish that shows two sexually distinct types of males: small gonochoristic males and large sex‐changed males. Large males defend specific mating sites above which females come to spawn. In such a mating system (pair spawning performed only by large territorial males), small males almost never get the opportunity to spawn. In a similar situation, Thalassoma bifasciatum, a coral reef species, shows a change of its mating system due to the influence of population density. As the population density grows, the proportion of small males in the population increases until they are numerous enough to take over a mating site where they perform group spawns. Concerning Thalassoma pavo, neither the group spawning behavior nor any other factor has ever been described to explain the maintenance of the two types of males.

Life History and Ecology of the Orangefin Darter Etheostoma bellum (Pisces: Percidae)

-The life history and ecology of the orangefin darter Etheostoma bellum were studied in the Green River system, Kentucky, from 1982 to 1987. Juveniles and adults were segregated mainly by water depth, current velocity and substrate type. Use of riffle habitats varied in relation to spawning activity. Sexual maturity was typically achieved at 2 yr of age; however, maturity was attained by some early-hatched 1-yr-olds. Spawning was from late April to late June in gravel substrates of fast-flowing riffles. Large territorial males spawned over females buried in the gravel, and on one occasion cuckoldry was observed. Average number of mature ova was 41; mean diameter of mature ova was 1.58 mm. Incubation time was 7-9 days at 23 C and mean total length at hatching was 6.1 mm total length. Males grew more rapidly and attained a larger size than females; maximum longevity was ca. 36 mo. Sex ratio of males to females was 1.05:1.00. Mean density was 0.5 fish/M2 but varied seasonally. Juveniles and adults ate mainly dipteran larvae, ephemeropterans and hydracarinians but selectivity of food items varied seasonally. Diel feeding patterns were bimodal and crepuscular in summer with peak activities at 1800 h and 2400 h.

Drastic effects of El Ni�o on Galapagos pinnipeds

Population dynamics of pinnipeds living in the tropical upwelling ecosystem of the Galapagos were strongly influenced by the 1982-83 Southern Oscillation-El Niño (EN) event which was the strongest recorded in this century. The Galapagos fur seal (Arctocephalus galapagoensis) population lost the four youngest year classes (1980-1983) almost entirely and approximately 30% of the adult females and non-territorial males. Mortality of large territorial males was almost 100%. Most of the 1982 year class of Galapagos sea lions (Zalophus californianus wollebaeki) died and there was a much lower pup production in the breeding season following EN. Recurrent EN events must strongly influence age structure and average population size of these and other otariid species depending on tropical upwelling ecosystems.

Territoriality, Body Size, and Spacing in Males of the Beewolf Philanthus Basilaris (Hymenoptera; Sphecidae)

Abstract1. Males of the digger wasp Philanthus basilaris defend and scent-mark small mating territories. There is a high rate of turnover of males on territories on both a daily and seasonal basis due, in part, to predation on territorial males and the large number of usurpations of territories. 2. The outcome of aggressive interactions on territories is determined by size differences among males, rather than by their status as resident or intruder. As a result, territory holders are larger on average than non-territorial males. The latter, however, remain in the area and attempt to usurp territories or replace residents that have abandoned their perches. Evidence suggests that larger territorial males are also less subject to predation by robberflies and conspecific females. 3. The type of mating system of this species resembles those defined as leks. Males established territories in groups of up to about 50. Nests of females were not found within aggregations of territories. There is a high potential for polygyny due to the lack of maternal care of offspring, dominance interactions which consistently favor larger males and result in intense sexual selection, and asynchronous emergence of females combined with potentially longlived males. Although large males are dominant, no body size related spatial structure to the aggregations could be identified. Aggregations of territories often occur in the same location from year to year, even though males live for only one season.

Mating Systems, Sex Change and Sexual Demography in the Rainbow Wrasse, Thalassoma lucasanum

Previous work indicates that sex change becomes less advantageous and less common in fish species which live at relatively high population densities. This study extends these observations to the abundant rainbow wrasse (Thalassoma lucasanum) of the eastern tropical Pacific. In this species, large territorial males in terminal phase coloration are uncommon, and the overwhelming majority of spawnings occur in groups of smaller initial phase males. For T. lucasanum, sex change itself is a relatively rare event; fewer than 30% of the terminal phase individuals are derived from females. The initial phase population consists of nearly 50% primary males, their theoretical maximum abundance. Laboratory experiments indicate that sex and color change is socially mediated: the largest individual changed color (and sex if she was a female) in ten groups initiated without a terminal phase male, while no transformations occurred in 15 control groups. The retention of sex-changing ability should carry little or no cost even in densely distributed populations, and can be of great advantage in any small groups that might exist. In addition to ensuring proper timing of transformation in small groups, social mediation of sex change may be of value in preventing sex change from occurring at all in situations where the costs of transformation are too great.