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Male–Male Strategies copulation (precopulatory male–male competi- tion), between copulation and fertilization Martin Reichard (postcopulatory male–male competition), or after Academy of Sciences of the Czech Republic, fertilization. While it has long been believed that Praha, Czech Republic male–male competition and female choice are mutually reinforcing, research in recent decades suggests that it is often not the case. Synonyms

Male intra-sexual competition; Male–male Forms of Male-Male Competition contest Traits that undergo sexual selection are sometimes divided between armaments (weapons used in Definition male–male contests and signals of male fighting ability – status badges) and ornaments (signaling Direct or indirect competitive interactions over traits used by females in mate choice decisions). access to females, their gametes or resources to However, many sexually selected traits have a attract females. dual function and are clearly affected by both forms of sexual selection (Andersson 1994). It appears that many sexually selected traits may Introduction have initially undergone selection in the context of male–male contests and then have subse- Male–male competition is, along with female quently been adopted by females as a signal of choice, one of two main mechanisms of sexual male quality. This is because male weapons are selection (Darwin 1871; Andersson 1994). How- honest “signals” of male fighting ability since they ever, male–male competition has received much are routinely put to trial during male contests. less theoretical end empirical interest than female Such traits can then be reinforced through female mate choice, perhaps because it is conceptually choice, with both intra- and intersexual selection more straightforward and easier to comprehend driving the evolution of the trait. The reverse (Parker 2014). Competition among males that process can also be true. Thus, traits traditionally increases their fitness (reproductive success) is viewed as ornaments that have been selected performed to increase an individual’s access to through female choice may be used by males in females or their eggs. It is manifested before aggressive displays, including such traits as bright

# Springer International Publishing Switzerland 2016 T.K. Shackelford, V.A. Weekes-Shackelford (eds.), Encyclopedia of Evolutionary Psychological Science, DOI 10.1007/978-3-319-16999-6_108-1 2 Male–Male Strategies coloration and elaborated body appendages the contest is not resolved with these displays, the (Berglund et al. 1996). contest escalates, with attempts to bite the oppo- The two mechanisms of sexual selection need nent’s fins and flanks. If the contest is still not not always be mutually reinforcing. Recent resolved, males may lock jaws, sometimes research documented that male–male competition remaining in this position for several minutes and female choice can act in concert, independent (Polačik and Reichard 2009) and with potentially of each other or in opposition. A common illus- fatal consequences for one of the combatants. tration of concerted evolution is male coloration. Larger body size or body mass is perhaps the For example, red nuptial coloration in the male most obvious and probably most common trait three-spined stickleback fish (Gasterosteus that is selected through male–male interference aculeatus) appears to be selected through competition. Body size is a good predictor of male–male competition and female choice. Red overall physical strength and performance coloration is a characteristic of dominant individ- (McCullough and Simmons 2016). In staged con- uals that win fights, and females prefer to mate tests, larger males enjoy a substantial advantage, with redder males. Additionally, variation in red- and body size/mass is often the clearest predictor ness increases under male–male competition and of the outcome of a contest, though it is often this may facilitate female choice (Candolin 2000). correlated with other traits that may contribute to In contrast, conflicting selection pressures are success. involved in the production of social pheromones Many direct male–male contests rely on the by males of the speckled cockroach (Nauphoeta use of weaponry. Weapons such as horns, antlers, cinerea), with differences in male–male competi- spurs, enlarged jaws and teeth, and other body tion and female attraction signaling optima. structures and appendages are used to directly Hence, male cockroaches with a pheromone outcompete an opponent. At the same time, level that enables them to gain a dominant posi- weapons often serve as a signal of fighting ability tion are not preferred by females (Moore and (badge of status) and are used during the signaling Moore 1999). stage of a contest. Only when any of the rivals The form of male–male competition varies retreats from the signaling contest, a physical widely among taxa and mating system. The most interference follows. For example, male red deer obvious is male–male interference competition. It fight over possession of females with rivals wres- is manifested as a physical contest (direct fight), tling with their antlers and attempting to push each signaling contest (ritualized fight in which an other away. Fights in other species may involve individual matches themselves against an oppo- pushing, pulling, or dislodging an opponent. The nent via the expression or display of signal traits), size of weaponry is often associated with body or a combination of both. Most direct fights ensue size and both may be indicators of overall male when a signaling contest does not lead to a clear condition (Andersson 1994). Fighting is costly winner. For example, male African annual fishes and potentially lethal, and many contests are (genus Nothobranchius) compete for access to resolved at the signaling stage despite males females by rapidly approaching an opponent and possessing formidable weapons. In the case of performing lateral displays that involves spread- red deer, rival males walk in parallel and assess ing the unpaired fins. Males are brightly colored the opponent’s antlers and body size. It is only and coloration and body size usually determine when neither male backs down from a contest that the winner of the contest at the signaling stage. a fight with antlers occurs, potentially with serious Lateral displays expose bright coloration and injuries. include tail beating, which directs a stream of Other traits selected through male–male com- water toward the opponent, and mutual threats petition have a primarily signaling function. performed with prominently displayed While they vary more widely than traits used in branchiostegal membranes (Passos et al. 2015). direct contests, they supposedly also indicate When the difference between males is small and overall individual performance. Acoustic and Male–Male Strategies 3 visual displays are the best researched signaling considerable survival costs by attracting enemies traits, though chemical traits appear more com- exploiting signal transmission such predators or mon that generally assumed, and other modalities, parasitoids (Zuk and Kolluru 1998). Third, there such as electrical discharges in electric knife are indirect costs that include energy depletion fishes (Gymnotiformes), are known to serve for (allocation of resources to the trait expression signaling individual characteristics. The function traded off against its use in somatic maintenance, of most signals in the context of male–male com- immunocompetence, or sperm production). petition is intimidation. Hence, many such traits Fourth, increased expression of factors within tend to be exaggerated. Yet, for a signal to be particular hormonal pathways that are function- evolutionary stable, it must carry honest informa- ally essential for the expression of the trait or tion about the status of the signaler: his physical signal can be costly for other phenotypic functions strength, body size, condition or prior residence, (Blagosklonny 2008). Hence, optimal trait and ownership of a breeding resource. For exam- expression to maximize lifetime fitness ple, some aspects of the vocal signals of male red (reproductive success and survival) is often deer (minimum formant frequencies) are much lower than the maximum potential expres- constrained by individual anatomical features, sion of the trait. directly associated with male body size. Hence, Lekking males compete for access to females it provides receivers with accurate information by via displays, aggregating in large numbers in spe- which they can measure a rival’s competitive abil- cific spots visited by females. Lekking is rela- ity (Reby and McComb 2003). Signaling male tively widespread among insect, fish, and bird fighting ability, however, may also include subtler species, but also recorded in other taxa such as signals. Cuticles of most terrestrial arthropods mammals. Male–male competition on leks is contain cuticular hydrocarbons, semiochemicals severe, leading to high variance of male mating with extensive within-species variation (Ingleby success. It is generally assumed that reproductive 2015). Cuticular hydrocarbons convey complex success of males in leks depends on female information about an individual, including infor- choice, but competition to obtain a display site mation on male competitive ability. Indeed the on the lek and for the best positions within the lek composition of these chemical signals can have a also contributes to male success (DuVal and profound influence on the outcome of male–male Kempenaers 2008). For example, in black grouse competition (Lane et al. 2016). (Lyrurus tetrix), lekking males fight frequently The expression of weapons and signal traits and successful males experience high success may be constrained by direct and indirect costs. (Hämäläinen et al. 2012). First, direct costs arise from increased risk of Endurance is an important, but often damage or mortality. In the Asian rhinoceros bee- overlooked, aspect of male–male competition tle (Trypoxylus dichotomus), the risk of breakage and describes the temporal component of is highest for the longest horns, and overly large male–male competition. To be successful, domi- horns may, therefore, constrain selection on the nant males must maintain their high rank across a continued exaggeration of horn length driven by time span of days, weeks, months, or even years. male–male competition by setting a mechanical The length of the breeding season varies widely limit on maximum horn size (McCullough 2014). among taxa, environments, and geographic Second, exaggerated signals of male–male com- regions. Highly seasonal environments often petition ability may incur a cost of increased pre- have a breeding season confined to a relatively dation by reducing escape ability or increasing short period when most fertilizations occur. In detectability by predators. In T. dichotomus, other taxa and less seasonal regions and environ- males with larger horns suffer significantly higher ments, fertilizations may occur throughout the predation rates from avian and mammalian pred- year. Male–male interference competition is typi- ators (Kojima et al. 2014). Likewise, many con- cally highest when female receptivity is tempo- spicuous signals of different modalities carry rally clustered within a short period, and the most 4 Male–Male Strategies successful male may secure a large number of male fitness and imposes selection on superior fertilizations. However, this scenario is also sensory ability and locomotor organs. Hence, the prone to the evolution of alternative mating most mobile males in a population can mate with behaviors when some males circumvent direct more females, outcompeting less mobile males. In competition with the highest-ranked males and red-spotted newts (Notophthalmus viridescens), undermine their ability to control access to tail size is associated with locomotory capacity, females. Dominant males typically cannot and males with the largest tails have the greatest monopolize all females when they are unable to mating success, possibly due to higher ability to control their spatial distribution (Reichard capture females (Able 1999). In many arthropods, et al. 2005). males have larger eyes, antennae, and other sen- Harems are examples of mating systems with sory organs than females which have presumably low temporal clustering of female receptivity evolved as an adaptation to locate mates, indi- combined with an elevated importance of rectly pointing toward the importance of scramble male–male competition for reproductive success. male–male competition. A temporal component is Possession of a harem is physiologically demand- intrinsically important in scramble competition, ing and potentially costly to the territory holder and in many anurans (toads and frogs), males through frequent contests with rival males. Harem intercept females already on their way to a breed- holders (and alpha males in social groups with ing pond and clasp them in amplexus to secure subordinate males) stage many contests from early access to females. rivals for their position, and there may be substan- Male–male competition for reproductive suc- tial turnover of individual males in the possession cess goes beyond direct interference, even at the of the top rank. Defense of harems increases premating stage. In many mating systems, some immediate reproductive success (the number of males can circumvent direct male–male competi- progeny) but has longer-term consequences for tion by alternative mating behaviors (AMB). survival and may lead to rapid reproductive senes- AMB are behavioral adaptations that enable cence (Lemaître et al. 2014). males to compete with their rivals (and sometimes Mate guarding is another mechanism of outcompete them) through the use of behavior that male–male competition. In some taxa, males is different from the “typical” male–male interfer- restrain female association with other males to ence competition. The most common examples ensure paternity of their offspring is not are sneak copulations (in internally fertilizing spe- compromised. Males may simply remain in close cies) or sneak fertilizations (in species with exter- proximity to a female and attempt to repel any nal fertilization). When sneaking, a male deceives rivals. Sometimes, mate guarding involves his rival and his access to a female is typically prolonged or repeated mounting of a female, cryptic, at least until copulation/gamete release. despite no further sperm transfer (Baxter Sneak male deception takes the form of camou- et al. 2015). For example, in the bug Lygaeus flage of their external appearance (female-like equestris, pairs can remain in copula for over appearance), hiding in a structured environment, 15 h and regularly move and feed in this position, or their combination. For example, in bluegill with males walking backward or being dragged sunfish (Lepomis macrochirus), males may along. Still, only a period of 1–2 h is needed for develop either into a territorial male that sexually successful insemination (Alcock 1994), and the matures at the age of 7 years and invests in terri- remaining time spent on copulation is probably a tory defense, nest construction, female courtship, form of mate guarding that reduces the likelihood and parental care. Alternatively, males may of female remating. mature when only 2 years old as a sneaker and Scramble competition for access to females is a compete with parental males (and other sneakers) frequent, though relatively rarely examined, form for fertilization. Young sneaker males “streak” of male–male competition. Successful searches into the nest of a territorial male during female for available females may considerably increase egg laying and may fertilize a subset of eggs Male–Male Strategies 5 before being chased away by the territorial male. males by sneaking fertilizations when young and Older sneaker males mimic female behavior and start to compete for breeding resources when they coloration and deceive territorial males into iden- grow older and larger (Wootton and Smith 2015). tifying them as a second female in the nest (Neff Yet, in some of these cases, especially in short- and Gross 2001). living species, differences in body size among A traditional view of male–male competition males are relatively small, and each male is capa- considers sneakers to be of low quality, incapable ble of playing the role of territorial and sneak of winning contests and therefore making “the male, with switches between the tactics within best of a bad job” to gain any reproductive suc- seconds. In the European bitterling, individual cess. However, there is now good evidence from males frequently switch between territorial and several mating systems to suggest that females sneaking behavior, often in a time span of sometimes prefer to mate with sneaker males. By minutes. They attract females to their own breed- preferring sneaker males, females avoid limitation ing territory and, at the same time, attempt to of the expression of their mating preferences by sneak-fertilize the eggs of females laid in the resource monopolization by males wining con- territories of neighboring males (Reichard tests over breeding resources. This leads to an et al. 2004). In general, the success of alternative incongruence between male–male competition mating behavior is dependent on demography and female choice where female choice is affect- (ratio between males and females, population den- ing the final outcome of male–male competition sity, male morphs density), environmental condi- (Reichard et al. 2007). In European bitterling fish tions (habitat complexity and ability to hide), and (Rhodeus amarus), males defend territories with the female response to alternative mating behavior living freshwater mussels into which females (Reichard et al. 2007). deposit their eggs. A limited number of dominant Finally, male–male competition may extend males may control most oviposition sites, forcing beyond fertilization. In the bluegill sunfish, terri- females to lay the eggs in their territories, despite a torial males care for the offspring for several days. mate choice preference for other males who have Parental males in this species are often cuckolded not acquired their own territory. Bitterling females by sneakers. However, they have the capacity to sometimes actively engage in a conspicuous assess their paternity level using the visual pres- behavior that attracts sneaking males and increase ence of parasitic sneaker males during spawning the time window for the eggs to be fertilized and, in addition, using olfactory cues released (Smith and Reichard 2005), modifying the out- from the offspring after the eggs hatched. Parental come of male–male competition when males are males dynamically adjust their parental care and of unequal competitive ability but when resource cannibalize those clutches for which their pater- defense is crucial for breeding. nity share is low (Neff 2003). Another example of Alternative mating behavior may have a male–male competition after fertilization can be genetic basis, depending on the developmental found in the three-spined stickleback. Male stick- stage or age, or may be entirely flexible and con- leback signaling effort (red body coloration) actu- text dependent. In ruff (Philomachus pugnax), ally increases during the post-mating period when satellite males tend to steal copulations from dom- males fully engage in parental care and no new inant males and “faeder” males mimic females. partners or fertilizations can be obtained. Parental Both alternative male forms differ conspicuously care is exclusively paternal in this species, and in behavior and coloration from dominant males male bright coloration may indicate his ability and the forms are genetically determined. Each and motivation to defend the nest and offspring alternative male morph possesses a unique, against competing intruders that might steal or non-recombining chromosomal inversion cannibalize the nest (Candolin and Tukiainen (Küpper et al. 2016). In many fish (and other) 2015). mating systems with breeding resource defense The relative importance of male–male compe- (i.e., nesting sites), males compete with other tition for reproductive success arises from 6 Male–Male Strategies variation in resource investment, parental care, Cross-References fertilization mode, and other parameters. In mat- ing systems with no male contribution to postferti- ▶ Copulatory Intrasexual Competition lization reproductive effort, the largest or ▶ Direct Male to Male Battles for Females strongest males secure access to a large number ▶ Lekking of females in harems. In contrast, when high ▶ Multiple Matings parental effort is needed for raising the offspring ▶ Precopulatory Intrasexual Competition successfully, stable pairs are formed, and the ▶ Sneak Copulation importance of male–male competition for fertili- ▶ Sperm Competition zation is low or restricted to postcopulatory pro- ▶ Vocal Competition cesses. In mating systems with pair bonds, males may compete for the access to females with the highest reproductive value (i.e., fertility), though References pairing in such systems is generally relatively unrestricted by mate coercion and dominated by Able, D. J. (1999). Scramble competition selects for greater female or mutual mate choice rather than direct tailfin size in male red-spotted newts (Amphibia: male–male competition. Salamandridae). Behavioral Ecology and Sociobiol- ogy, 46(6), 423–428. Alcock, J. (1994). Postinsemination associations between males and females in insects: The mate-guarding hypothesis. 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Changes in expression and honesty of tition involves direct physical or signaling con- sexual signalling over the reproductive lifetime of tests between males, with development of sticklebacks. Proceedings of the Royal Society London B, 267(1460), 2425–2430. weapons and expression of signals being Candolin, U., & Tukiainen, I. (2015). The sexual selection constrained by direct and indirect costs associated paradigm: have we overlooked other mechanisms in the with their possession. Other forms of male–male evolution of male ornaments? Proceedings of the Royal competition include scramble competition for Society London B, 282(1816), 20151987. Darwin, C. (1871). The descent of man and selection in access to females, lekking, mate guarding, and relation to sex. London: John Murray. alternative mating behaviors (e.g., sneak copula- DuVal, E. H., & Kempenaers, B. (2008). 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