Devoted fathers or selfish lovers? Conflict between mating effort and parental care in a harem‐defending arachnid

When there is a temporal trade‐off between mating effort and parental care, theoretical models predict that intense sexual selection on males leads to reduced paternal care. Thus, high‐quality males should invest more in mating effort because they have higher chances of acquiring mates, whereas low‐quality males should bias their investment towards parental care. Once paternal care has evolved, offspring value should also influence males’ decisions to invest in offspring attendance. Here, we performed a manipulation under field conditions to investigate the factors that influence male allocation in either mating effort or parental care. We predicted that facultative paternal care in the harem‐holding harvestman Serracutisoma proximum would be negatively influenced by male attractiveness and positively influenced by offspring value. We found that attractive males were less likely to engage in egg attendance and that the higher the perceived paternity, the higher the caring frequency. Finally, egg mortality was not related to caring frequency by males, but predation pressure was much lower than that recorded in previous studies with the same population. Thus, the benefits of facultative male care may be conditional to temporal variation in the intensity of egg predation. In conclusion, males adjust their investment in either territory defence or egg attendance according to their recent mating history and perceived paternity. Our findings suggest that exclusive paternal care can evolve from facultative paternal care only if the trade‐off between mating effort and parental care is circumvented.     

Food transfers to young and mates in wild owl monkeys (Aotus azarai)

Accounts of food sharing within natural populations of mammals have focused on transfers to offspring or transfers of food items that are difficult to obtain (such as meat). Five groups of socially monogamous owl monkeys (Aotus azarai azarai) in Formosa, Argentina were observed during 107 hr to determine the pattern of food sharing under natural conditions. There were a total of 42 social interactions involving food with food being transferred on eight occasions. Adult males transferred food to young more often than did adult females. All types of food that were readily obtained and eaten by all age/sex classes were transferred to young. Adult females also transferred food to their mates. This type of food sharing is very rare among animals and may have social benefits specific to monogamous mammals with paternal care.     

Size-related mating and mate guarding in the orb-web spiderNephila clavata (Araneae,Araneidae)

The orb-web spiderNephila clavata satisfies three conditions for assortative mating proposed by Ridley (The Explanation of Organic Diversity. The Comparative Method and Adaptations for Mating, Clarendon, Oxford, 1983); (1) a large male advantage in male-male competition, (2) a correlation between female size and fecundity, and (3) a long pairing duration. To test Ridley's hypothesis, size assortative mating and guarding were examined in the field. When data were pooled over time, assortative mating was found but this was due to temporal covariation of body sizes of males and receptive females. After controlling for the effect of time, size assortative guarding was not detected, although females guarded by males were larger than those not guarded in the early breeding season. Possible reasons for the absence of size assortative guarding were discussed.     

Female egg dumping and the effect of sex ratio on male egg carrying in a coreid bug

Phyllomorpha laciniata Vill (Heteroptera, Coreidae) is uniqueamong terrestrial insects in that females glue eggs on the backsof other conspecifics. Egg carrying byP. laciniatamales haspreviously been considered as paternal care. We explored femaleoviposition with respect to previous mating experience of femalesand tested whether sex ratio affects male egg-carrying. Thehypothesis that male egg-carrying is a form of paternal carepredicts that a male should always accept eggs after matingwith a female. However, if male egg-carrying is a form of postcopulatorymate guarding rather than paternal care, egg carrying shouldincrease in the presence of other males. When two couples wereplaced together, females laid eggs on the backs of all individualsenclosed, including the backs of other females. However, whena female was accompanied by 2 males, 22 out of 26 females ovipositedon their mating partner. Thus, sexual competition rather thanpaternity alone, affects a male's eagerness to carry eggs. However,even if males sometimes carry their own eggs, females lay eggson the backs of all conspecifics they can easily acquire. Thus,egg carrying in P. laciniata is partially voluntary and partiallythe result of female egg dumping     

The male's dilemma: Increased offspring production is more paternity to steal

Summary Large potential effects of male care on the number of offspring females successfully raise are not sufficient to select for caring males because of the pervasive importance of mating competition. Males face a version of the social dilemma, in which increased production increases the pay-off for theft. Models of the allocation of male effort partitioned between caring for babies and competing for paternity show that the optimal allocation to care is very low under a wide range of conditions. Like sex allocation where the alternatives are male versus female function or sons versus daughters, the pay-offs to one alternative are always strongly frequency dependent. Because that alternative (male function, sons, male mating effort) pays so well when rare, it cannot remain rare under most conditions. Here we consider the consequences of partitioning mating effort into mate guarding and all other forms of mating conflict. If a male gets all his partner's conceptions while guarding, gaining them at a constant rate, there are two possible regions of stability. The evolutionarily stable strategy (ESS) depends on a parameter scaling the decisiveness of (non-guarding) mating conflict. When marginal returns from conflict decrease with scale, almost all effort goes into guarding. When marginal returns increase, the ESS devotes all effort to mating. Even when the potential effect of care is large, male equilibrium strategies allocate little effort to it. We also report the results of computer simulations showing that care increases if gains from guarding saturate quickly, so that a male is assured of the paternity of most of his partner's offspring with little guarding, and consequently the pool of unguarded conceptions open to competion shrinks sharply. But even when the male's dilemma is very much reduced, it still substantially limits the allocation to care. The results of both computer simulations and mathematical analysis converge with other lines of evidence that mating has much stronger effects than parenting in shaping male strategies.     

Pre-oviposition mate-guarding and mating behaviour of Argia vivida (Odonata: Coenagrionidae)

Abstract. 1. At Halcyon Hotsprings, British Columbia, Canada, male and female Argia vivida Hagen encountered to mate in two different ways.
2. In the morning (before 12.30 hours solar time), males basked at sunspots in the forest and darted out at passing females, attempting to take them in tandem (the first method of encounter).
3. If a male was successful, the pair engaged in a 31.3±4.8 min copulation followed by an hour of tandem flight before beginning oviposition.
4. As the day progressed, unmated males moved slowly toward the water and arrived at the water at about the same time as the earliest ovipositing pairs (1131±27.5 min solar time).
5. Males retained their grasp on their mates during oviposition (contact-guarding) but since some tandems separated during oviposition, non-tandem males at the water could capture recently released, gravid females (the second method of encounter).
6. The new pairs performed a brief copulation (10.2±3.38 min) and began ovipositing immediately thereafter.
7. Some females that avoided recapture attempted to oviposit unguarded.
8. We believe the long duration of morning copulations and period of tandem constitute a male strategy, which we call 'pre-oviposition guarding', to guard females until it is warm enough at the oviposition site for the females to begin ovipositing.
9. Separation of tandems during oviposition may be initiated by either member of the pair and we suggest that one benefit to a female of leaving a guarding mate is increased efficiency of oviposition when the intensity of male harassment is low.
10. The mating system of A. vivida thus comprises a series of complementary male and female mating behaviours.     

Monogamy on the fast track

Social monogamy has evolved multiple times and is particularly common in birds. It is not well understood why some of these species are continuously and permanently paired while others occasionally 'divorce' (switch partners). Although several hypotheses have been considered, experimental tests are uncommon. Estrildid finches are thought to be permanently paired because being short-lived opportunistic breeders, they cannot afford the time to form a new pair relationship. Here it is shown through a controlled experimental manipulation that zebra finches (Taeniopygia guttata) allowed to remain with their partners to breed again are faster to initiate a clutch (by approx. 3 days) than birds separated from their mates that have to re-pair, supporting the hypothesis that continuous pairing speeds up initiation of reproduction, a benefit of long-term monogamy in a small, short-lived, gregarious species.     

Divergence in male mating tactics between two populations of the soapberry bug: I. Guarding versus nonguarding

I compared male allocation to prolonged mate guarding versusnot guarding between two populations of the soapberry bug (Jaderahaematoloma) that differ in adult sex ratio: Oklahoma, USA (mean± SD adult sex ratio, 2.70 ± 0.95 males per female),and Florida, USA (1.09 ± 0.26 males per female). To predictthe reproductive performance of each mating tactic in each population,I collected data on search time per mating, time required forguarding to be effective, sperm competition, female rematingpropensity, and female resistance to guarding. Search time alonediffered significantly between the populations, being much greaterin Oklahoma (estimated as 26.2 h per mate) than in Florida (estimatedas 9.6 h per mate). For males in each region, these data wereused to model the costs and benefits of guarding for differentnumbers of oviposition bouts versus not guarding. The reproductiverate of nonguarders in Oklahoma is exceeded by that of guarderswho remain with a female for more than one oviposition bout,but in Florida, the reproductive rate of nonguarders is onlyexceeded by that of guarders who remain with a female for atleast three ovipositions. Consistent with the model, Oklahomamales in field arenas guarded more frequently than did Floridamales. However, nonguarding was common in both populations,and guarding durations were highly variable.     

Strategic mate‐guarding behaviour in ladybirds

Mate‐guarding behaviour is regarded as a means of increasing paternity share by reducing sperm competition. It is known to be a plastic response which varies with operational sex ratios and competitor presence in the vicinity. In a recent study, prolonged mating duration in Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae) has been found to incorporate mate‐guarding behaviour. The present investigation was conducted to assess its plasticity in the presence of competitors. The physical and chemical presence of competitors of both sexes at varying densities was provided to a pair of ladybirds, and their time to commence mating, latent period and mate‐guarding duration was observed. These were compared to a control treatment where other partners were absent. All treatments were conducted with sibling as well as non‐sibling competitors. It was our hypothesis that mate guarding would be increased in the presence of male competitors and would be reduced by female presence. The results revealed that while mate‐guarding duration was increased by the chemical presence of males it was decreased by their physical presence. The latter result was attributed to interference by other males who dislodge the mating male in order to access the female. Female chemical presence had no effect on mate guarding, while physical presence increased the duration of mate guarding. The reasons for the latter behaviour require further investigation. Responses were not significantly affected by the relationship between the focal pair and the competitor. The authenticity of the mate guarding in this ladybird is strongly affirmed by our results.     

Male-male competition and mating success in the orb-web spider,Nephila clavata,with reference to temporal factors

Seasonal occurrence patterns of adults of both sexes, intensity of male-male interactions, and mating success in the spider,Nephila clavata, were examined in the field. Adult males began to attend female webs about 2 weeks before female maturation. Large adult males were abundant in the early breeding season, but small males increased later in the season. From the distribution of males among female webs and size relationship of males within a web, male-male interactions seemed to be more intense when most females were still subadult. This was verified by a field experiment in which males were artificially introduced to female webs that were attended by other males. It was found that the probability of introduced males remaining on subadult female webs was lower than that on adult webs. As mating occurred mostly in the period shortly after the female final molt and first male sperm precedence was known in all spiders reported so far, intense male-male competition on subadult female webs seemed to be reasonable. Male longevity had an important influence on the mating success of males with just-molted females. Mating success was also affected by the relative body size of males present in a given period. Since larger males occupied the position closest to females within a web and stayed there longer, relative body size appeared to influence mating success through male-male competition. Female body size at maturation declined with time; hence, males that attained sexual maturity earlier had the advantage of mating with larger and more fecund females. Therefore, early maturation as well as larger size seem to be two important trairs influencing the reproductive success of males.     

Flexible Mate Guarding Tactics in the Dragonfly Sympelrum Internum (Odonata: Libellulidae)

Mate guarding–a behaviour prevalent in odonates–is a post copulatory association during which males prevent females from re-mating. Some species use two forms of guarding: contact mate guarding, which is energetically costly but highly effective and non-contact mate guarding, which is less costly but less effective. This study aimed to determine if male Sympetrum internum (Odonata:Libellulidae) adjust the duration of contact mate guarding according to environmental, temporal and physiological factors. There was a significant interaction between male density and season on duration of contact mate guarding. Early in the season males increased the duration of contact guarding as the density of rivals increased. Later in the season males guarded mates longer irrespective of male density. Wind and temperature did not detectabiy alter the duration of contact mate guarding, suggesting that the trade-off between current and future reproductive success was more important than were physiological costs.     

Sex in a cyclical parthenogen: mating behaviour of Chydorus sphaericus (Crustacea; Branchiopoda; Anomopoda)

1. We describe the interactions during mating in Chydorus sphaericus, a cyclical parthenogenetic anomopod. Mating behaviour is more complex than previously assumed, with evidence for a diffusible chemical to which males react at the onset of mating, for reproductive isolation, and for postcopulatory mate guarding. 2. During mating, the male and female form a ‘mating cross’ that may be maintained for several hours, while copulation itself typically lasts less than a minute. Furthermore, males invariably attach to the right valve of females. Copulation involves intromission of the postabdomen between the valves, so that the gonopores approach the left ovarium. 3. This behaviour is reflected in the morphology of both sexes: males have a specialised anterior valve margin, postabdomen, first limb and rostrum, under selective pressure for successful mate guarding and copulation, while gamogenetic females have asymmetric ovaries, and a species‐specific setulation of the valves. Males of the structurally related Chydorus ovalis react to the presence of C. sphaericus, but fail to dock to females, suggesting a lock‐antilock element in the reproductive isolation of both species. 4. The morphological and ethological adaptations in C. sphaericus suggest that there is a strong selective pressure on mating behaviour in this cyclical parthenogen and specifically towards the formation of the ‘mating cross’.     

High mortality and female‐biased operational sex ratio result in low encounter rates and moderate polyandry in a spider

The taxonomy of the Old World bat genus Otomops (Chiroptera: Molossidae) has been the subject of considerable debate. The failure of classical morphological studies to provide consistent patterns regarding interspecific relationships within Otomops has limited any understanding of the evolutionary history of the genus. We used traditional and geometric morphometric approaches to establish the species limits of taxa from sub‐Saharan Africa, the Arabian Peninsula, and Madagascar. Morphometric data supported the recent recognition of three distinct Afrotropical taxa: Otomops madagascariensis from Madagascar; Otomops martiensseni s.s. from southern, eastern, central, and western Africa; and an undescribed taxon from north‐east Africa and the Arabian Peninsula. Analyses of craniodental measurements and landmark‐based data showed significant cranial size and shape divergence between the three taxa. Cranial size and shape variation within Afro‐Arabian Otomops were strongly influenced by altitude, seasonality of precipitation, and precipitation in the driest month. Based on morphometric patterns and molecular divergence estimates, we suggest that morphological evolution within Afro‐Arabian Otomops occurred in response to the fluctuating climate during the Pleistocene on the one hand, and the increasing aridity and seasonality over north‐eastern Africa on the other. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, •• , ••–••.     

Costs of intersexual conflict in the isopod Idotea baltica

In sexual reproduction one sex can increase its reproductive success at the cost of the other, a situation known as intersexual conflict. In the marine isopod Idotea baltica, males guard females before copulation. The guarding phase is preceded by struggles as females resist males’ attempts to initiate guarding. We determined whether the struggle and/or mate‐guarding result in fitness costs in the form of decreasing fecundity and lower levels of the energy storage compounds, glycogen and lipids. Females that underwent the period of struggles with males had decreased glycogen levels compared with females maintained alone. No such cost was found for males. Females guarded by a male also had smaller eggs than females that were not guarded. Thus the intersexual conflict, imposed by the fitness maximization strategy of the males, gave rise to both a fecundity cost and an energetic cost for females. The fecundity cost confirms the existence of intersexual conflict in I. baltica. This cost is shared by males, suggesting that the intersexual conflict restrains the reproductive output of both sexes.     

Explicit experimental evidence for the effectiveness of proximity as mate-guarding behaviour in reducing extra-pair fertilization in the Seychelles warbler

Extra-pair copulations (EPCs; copulations outside the pair bond) are widespread in birds and may result in extra-pair fertilizations (EPFs). To increase reproductive success, males should not only seek to gain EPFs, but also prevent their own females from gaining EPFs. Although males could reduce the number of EPCs by their mates, this does not necessarily mean that they reduce the number of EPFs; indeed several studies have found no association between EPCs and EPFs. Male Seychelles warblers (Acrocephalus sechellensis) follow their partner closely during the period when the pair female is most receptive (fertile period). We show that males that guarded their mates more closely were less likely to have extra-pair young in their nest. This study on the Seychelles warbler is the first to provide explicit experimental evidence that mate guarding is effective in reducing EPFs. First, in territories where free-living males were induced to stop mate guarding during the pair female's fertile period, extra-pair parentage was higher than in the control group. Second, in the experimental group, the probability of having an extra-pair nestling in the nest was positively associated with the number of days during the fertile period for which mate guarding was artificially stopped. Thus, male mate guarding was effective in reducing the risk of cuckoldry.     

Costs of Mate Guarding and Opportunistic Mating Among Wild Male Japanese Macaques

A trade-off relationship between mating and feeding effort is important when considering reproductive strategies of long-lived species. I compared the influence of male sexual activities, female mate-choice behaviors and the daily activity budget on male mating success among males in a group of wild Japanese macaques (Macaca fuscata yakui) on Yakushima Island. The 1st-ranking male, which had immigrated into the troop at this rank, more frequently approached peri-ovulatory females, spent more time grooming peri-ovulatory females and in mounting series and spent less time feeding than subordinate males did. The 1st-ranking male attained the highest mating success as a result of his high expenditure of time and energy in sexual behaviors directed toward peri-ovulatory females. Mating success of subordinate males did not relate to the amount of sexual effort, but instead to the frequency of female approaches, female rush toward males and the number of peri-ovulatory females within the group. The pattern of intermale competition shifted from nearly contest competition to scramble competition as the number of peri-ovulatory females in the group increased. Feeding time of subordinate males did not vary between the days when they copulated and the days when they did not. The findings demonstrate that mate guarding in the 1st-ranking male is a high-cost mating tactic, while opportunistic mating in subordinate males is a low-cost mating tactic. The differences in male mating tactics are probably related to male life history and to the formation of groups with a high socionomic sex ratio.     

An experimental test of mate choice for red carotenoid coloration in the marine copepod Tigriopus californicus

Colorful ornaments are hypothesized to have evolved in response to sexual selection for honest signals of individual quality that provide information about potential mates. Red carotenoid coloration is common in diverse groups, and in some vertebrate taxa, red coloration is a sexually selected trait whereby mates with the reddest ornaments are preferred . Despite being widespread among invertebrates, whether red carotenoid coloration is assessed during mate choice in these taxa is unclear. The marine copepod Tigriopus californicus displays red coloration from the accumulation of the carotenoid astaxanthin. Previous research on copepods has shown that astaxanthin provides protection from UV radiation and xenobiotic exposure and that carotenoid production is sensitive to external stressors. Because of the condition dependency of the red coloration, we hypothesized that Tigriopus would use it as a criterion during mate choice. To test this hypothesis, we conducted trials in which males chose between females that were wild-type red (carotenoid-rich algae diet) or white (carotenoid-deficient yeast diet). To control for dietary differences and to isolate the effect of carotenoid coloration, we also presented males with restored-red females fed a carotenoid-supplemented yeast diet. We found that wild-type red females were weakly preferred over white females. After controlling for diet, however, we found that restored-red females were avoided. Our observations do not support the hypothesis that male copepods prefer the carotenoid coloration of females during mate choice. We hypothesize that algal-derived compounds other than carotenoids play a role in mate choice. Red coloration in copepods appears to be a condition-dependent trait that is not assessed during mating.