Female red squirrels fit Williams' hypothesis of increasing reproductive effort with increasing age

Williams predicted that reproductive effort should increase as individuals age and their reproductive value declines. This simple prediction has proven difficult to test because conventional measures of energy expenditure on reproduction may not be a true reflection of reproductive effort. We investigated age-specific variation in female reproductive effort in a stable population of North American red squirrels where energy expenditure on reproduction is likely to reflect actual reproductive effort. We used seven measures of reproductive effort spanning conception to offspring weaning. We found that females completed growth by age 3 and that reproductive value decreased after this age likely because of reproductive and survival senescence. We therefore, predicted that reproductive effort would increase from age 3 onwards. The probability of breeding, litter mass at weaning, and likelihood of territory bequeathal were all lower for 1- and 2-year-old females than for females older than 3 years, the age at which growth is completed. That growing females are faced with additional energetic requirements might account for their lower allocation to reproduction as compared with older females. The probability of attempting a second reproduction within the same breeding season and the propensity to bequeath the territory to juveniles increased from 3 years of age onwards, indicating an increase in reproductive effort with age. We think this increase in reproductive effort is an adaptive response of females to declining reproductive values when ageing, thereby supporting Williams' prediction.     

Post‐weaning parental care increases fitness but is not heritable in North American red squirrels

Most empirical attempts to explain the evolution of parental care have focused on its costs and benefits (i.e. fitness consequences). In contrast, few investigations have been made of the other necessary prerequisite for evolutionary change, inheritance. Here, we examine the fitness consequences and heritability (h²) of a post‐weaning parental care behaviour (territory bequeathal) in a wild population of North American red squirrels. Each year, a subset (average across all years = 19%) of reproductive females bequeathed their territory to a dependent offspring. Bequeathing females experienced higher annual reproductive success and did not suffer a survival cost to themselves relative to those females retaining their territory. Bequeathing females thus realized higher relative annual fitness [ω = 1.18 ± 0.03 (SE)] than nonbequeathing females [ω = 0.96 ± 0.02 (SE)]. Additive genetic influences on bequeathal behaviour, however, were not significantly different from 0 (h² = 1.9 × 10^?3; 95% highest posterior density interval = 3.04 × 10^?8 to 0.37) and, in fact, bequeathal behaviour was not significantly repeatable (R = 2.0 × 10^?3; 95% HPD interval =0–0.27). In contrast, directional environmental influences were apparent. Females were more likely to bequeath in years following low food abundance and when food availability in the upcoming autumn was high. Despite an evident fitness benefit, a lack of heritable genetic variance will constrain evolution of this trait.     

Territorial bequeathal by red squirrel mothers

Red squirrels (Tamiasciurus hudsonicus) defend individual, food-basedterritories year round. These territories are crucial for overwintersurvival, yet some female red squirrels in northern populationsbequeath their territories to offspring and search for a newone. Bequeathal involves active, strategic dispersal by breedingfemales. Our study documents this unusual behavior and investigatesits correlates in two red squirrel populations in northern Canada.Thirty percent of breeding females dispersed. Bequeathal wasrelated to breeding date, with late-breeding females more oftendispersing, but was not related detectably to female conditionor territory quality. As an underlying trade-off, early-bornjuveniles more likely acquired a territory independently, butearly-breeding females lost mass and may have increased theirrisk of territory loss. We suggest that bequeathal has evolvedas a consequence of condition dependence in breeding date coupledwith limited resources.     

Personality, habitat use, and their consequences for survival in North American red squirrels Tamiasciurus hudsonicus

Personality affects many aspects of an individual's behaviour, life history and fitness, and has been shown to be moderately heritable in wild populations. Correlations between personality and risk‐taking that lead to life history tradeoffs could act to maintain variation in personality within a population, but this has not yet been tested. In this study, we used females from a marked population of North American red squirrels in Kluane, Yukon, to determine whether personality predicts risk‐taking in the wild, and whether these risk‐taking behaviours result in life history tradeoffs. We measured personality in open field and mirror image stimulation tests and extracted two traits, activity and aggressiveness, using principal component analysis and mixed model techniques. Using trapping records for individuals from February to September 2005, we obtained three measures of risk‐taking: the number of trapping events, the number of different trapping locations, and the maximum distance between the home territory and a trapping event. We used GLMs to determine whether the activity and aggressiveness of individuals are related to these risk‐taking behaviours, and found that active squirrels were trapped significantly more frequently and at a greater number of locations. There was also a significant interaction between activity and aggressiveness to affect the maximum capture distance. To determine if there are fitness tradeoffs associated with these risk‐taking behaviours, we examined female bequeathal behaviour and survival. Bequeathing a territory increases offspring probability of overwinter survival, and we found that an increasing number of trapping locations was associated with an increasing tendency to bequeath. Active females were less likely to survive until the following spring. Risk‐taking is therefore predicted by personality in this population, and they affect both survival and territorial bequeathal. These fitness tradeoffs may therefore lead to the maintenance of variation in personality.     

Microsatellite determination of male reproductive success in a natural population of the territorial ornate dragon lizard, Ctenophorus ornatus

It is now evident that the genetic mating system can be very different to the observed mating system. However, it is less well known what makes particular individuals more (or less) successful than expected from the observed system. In this study the observed territorial structure of a field population of the agamid lizard, Ctenophorus ornatus, was compared with the mating system as evidenced by microsatellite parentage assignment. This study also investigated whether any male traits predicted reproductive success. Sixty-five per cent of clutches were sired at least partially by a male other than the main territory-holding male and 35% of clutches were sired by a male with no overlap of the female's territory. Multiple paternity was moderately frequent at 25% of clutches. Male chest patch size predicted territory size and the number of females in the territory, but did not predict reproductive success. Instead, male head depth and body size were independently related to the number of offspring sired. As male head depth also predicted the number of females in a territory, these males are likely to be gaining increased reproductive success as a consequence of the higher number of females in their territories. Larger body size males, however, did not have a greater number of females in their territory and instead had more extra-territorial copulations. Whether these extra-territorial copulations are due to female choice or success in male competition is unknown.     

Intra- and Inter-seasonal Variation in the Socio-Spatial Behavior of Adult Male Collared Lizards, Crotaphytus collaris (Reptilia, Crotaphytidae)

When individuals maintain strong inter‐seasonal philopatry to the same territories, males may be able to re‐establish territory occupancy without intense intra‐sexual aggression, and instead spend more time courting females early in the reproductive season. Furthermore, when some males have prior experience defending the same territories, it may be necessary for young males to exhibit higher levels of aggression because they are establishing a territory for the first time. We tested these hypotheses by examining within‐season (1992 and 1997) temporal variation in the social behavior of adult male collared lizards of known age and prior territorial experience in a population where inter‐season philopatry to territories is high. Contrary to expectations, the frequency of aggression exhibited by males with and without prior territorial experience did not differ. The frequency of intra‐sexual aggression was higher in 1992 than in 1997, perhaps because male competitors were more abundant in 1992. Although there was an interactive effect of year, male display and patrol were low at the beginning of the reproductive season in Apr. and May, reached peaks during midseason in June, and then decreased as reproduction ended in July. The size of territories showed a similar pattern, with males defending larger areas in June. Our data support the philopatry hypothesis in that the establishment of territories occurred without high levels of aggression early in the season, perhaps because territory boundaries have been well defined by high rates of patrol and advertisement during the middle of the previous season. Inter‐sexual interactions were most frequent in June rather than at the beginning of the reproductive season. Adult females are producing their second clutches and yearling females are producing their first clutches in June. The high rate of inter‐sexual encounters in June supports the hypothesis that males allocate more time to courtship when females are receptive because there are more reproductively active females at this time. The temporal pattern of activities in adult Crotaphytus collaris appears to function as a compromise between competing intra‐ and inter‐sexual social demands on males, allowing males to maximize mating opportunities as well as maintain future access to productive territories.     

The Behavioral Significance of Male Body Size in the Tarantula Hawk Wasp Hemipepsis ustulata (Hymenoptera: Pompilidae)

Large males of the tarantula hawk wasp Hemipepsis ustulata appear to have an advantage in the competition for mates. Large males are more likely to acquire perch territories used to scan for incoming receptive females and territorial males appear more likely to mate than non‐territorial males. In addition, among the males that do secure a mate, those that intercept a female on a territory are larger than those that do so elsewhere. Despite the mating advantages apparently enjoyed by larger males of this species, average male size has remained essentially constant over the last 25 yr. Moreover, larger males are not seen to employ certain competitive tactics that might otherwise enhance their reproductive success. Thus, larger males did not preferentially visit the most popular landmark territory compared to a site that attracted fewer visitors overall. Nor were larger males more likely to return to potential territories after marking, capture, and release, either immediately or on a subsequent day. Finally, although large males made up a significantly greater proportion of the males captured at two territories as the 2005 flight season progressed, over all the years of the study, receptive females have not been concentrated in the latter part of the flight seasons.     

Age-specific variation in reproduction is largely explained by the timing of territory establishment in the New Zealand stitchbird Notiomystis cincta

1. Using data from 327 nests over a consecutive 8-year period we examined age-specific variation in reproduction in a population of stitchbirds (or hihi) Notiomystis cincta and related how differences in reproductive performance were linked to the timing of territory establishment and breeding. 2. Across the population all reproductive parameters showed a quadratic relationship with an increase mainly between the first and second breeding season and a decline after the fourth year. A longitudinal analysis showed evidence of senescence by the sixth year in the numbers of chicks fledged and recruited. 3. Reproductive increases between years 1 and 2 were the result of poor-quality females dying after their first breeding season (differential selection hypothesis) in combination with surviving females showing improvements in reproduction in their second year (individual improvement/constraint hypothesis). 4. There was no effect of mate experience or territory quality on improvements in breeding between years. 5. The key variable influencing reproductive output was the timing of breeding. Birds that started laying earlier were more likely to lay multiple clutches in any given season. This was the main difference between first-year and older birds; generally first-year birds initiated egg laying later and consequently laid fewer clutches. 6. Approximately half of all first-year birds did not establish their territory until after the breeding season had begun. This delay in territory establishment resulted in these birds delaying breeding, which resulted in them having a lower reproductive output relative to all other birds. First-year birds that managed to establish their territory before breeding commenced, had similar rates of reproduction as older birds. 7. There was a positive relationship between the timing of territory establishment during a female's first year and her hatching date in the previous breeding season. We hypothesize that this was because late-hatched females were less able to effectively compete for territories against earlier-hatched members of their cohort, and this delayed their establishment and breeding in their first year. Thus, this social constraint is likely to be a major factor driving age-specific reproductive variation in this population.     

Pairing strategies and mate choice in female robins Erithacus rubecula

Female European robins (Erithacus rubecula) adopted three different pairing strategies. These were, in order of frequency: moving on to a male's territory; fusing her territory with that of a neighbouring male; and being joined by a male on her territory. Although females were not free to choose between strategies during a particular season, individuals frequently changed strategy between different years. Their behaviour suggested that they were exercising mate choice, although the scope for such choice was limited by a strong tendency for a female to pair in areas where she had lived previously (her ‘Familiar Areas’). Males with large territories were more likely to pair and tended to pair earlier than those defending small territories. Female pairing strategy was also correlated with the area of their own territory. Although it is considered likely that some unidentified confounding variable was responsible for at least part of these relationships, possible causal explanations involving territory size are discussed. These include mate choice and a random settlement model. However the simplest explanation for the advantage enjoyed by males on large territories is that their territories were more likely to overlap with females' Familiar Areas.     

Early comers occupy popular territories in a lycaenid butterfly,Chrysozephyrus smaragdinus (Lepidoptera: Lycaenidae)

Territorial activities of a lycaenid butterfly, Chrysozephyrus smaragdinus, were observed throughout its adult season to investigate the territorial dynamics. The territories occupied earlier in the season were abandoned later than later‐occupied territories, indicating that the site preference of male C. smaragdinus was largely maintained during the adult season. Three indexes of territory quality based on animal preference, occupation duration (OD), initial occupation date (IOD) and the number of contests (NOC), were highly correlated. Therefore, these preference‐based indexes are consistent and reliable, although they are indirect estimates of benefits obtained from territories. Males arriving at territory sites early in the season were more likely to hold territories of better quality when NOC was used as the index of territory quality. The positive relationship between territory quality and male arrival date is congruent with the result of a previous study showing that early comers tend to hold a territory whereas late comers do not. However, male arrival date was not related to territory quality when OD or IOD was used as an index of territory quality. One possible reason for this apparent discrepancy is that the coefficient of variation of NOC is larger than those of OD and IOD, and therefore NOC could evaluate territory quality more quantitatively than the other two indexes. To date, studies of territoriality in butterflies have not considered the quality of territories. More studies considering the quality of territories will provide new insights into butterfly territoriality.     

Intraspecific competition and the maintenance of monogamy in tree swallows

Intraspecific competition for access to breeding resources maylimit male mating success typically monogamous birds. We examinedthe potential for intraspecific competition to limit polygynyin tree swallows at Beaverhill Lake, Alberta, Canada. In thispopulation, polygynous males raisedmore fledglings than monogamousmales, and there was little or no cost to females from nestingpolygynously. Under these conditions one might expect polygynyto be more common than that observed(8% of males). We foundthat females were most aggressive toward conspecific intrudersearly in the breeding season. This aggression was associatedwith (1) females settling farther apart than expected underrandom settlement, (2) later settlement by secondary than bymonogamous females, and (3) no relationship between female settlementdate and male territory size instead of the negative correlationexpected if females settled randomly without competition. Earlyin the season, males also settled farther apart than expectedif they had settled randomly, and among males with two or morenest boxes on their territory, males with widely separated nestboxes were more likely to be polygynous. Monogamy is probablythe most common pairing association in this population becauseintraspecific competition for nest sites prevents most malesfrom gaining a territory with nest sites far enough apart topermit two females to breed without one female excluding theother. Females appeared to be defending an area surroundingtheir nest box to limit nest usurpation or intraspecific broodparasitism, rather than to limit any loss of male parental carefrom polygyny.     

Age‐ and sex‐related differences in the spatial ecology of a dichromatic tropical python (Morelia viridis)

Abstract: Despite outnumbering their temperate counterparts, tropical snake species have been poorly studied. Yet, the few tropical species that have been studied show a variety of behavioural traits beyond those described in temperate species. Here we reveal both age and sexual differences in the movements of tropical green pythons (Morelia viridis: Pythonidae). We radio‐tracked 27 individuals (17 females and 10 males) for up to 18 months, locating individuals during both the day and night. The home range size for adult females (mean ± SE of 6.21 ± 1.85 ha) was correlated with snout–vent length. Neither adult males nor juveniles had a stable home range. Adult females had stable home ranges that overlapped considerably with those of other females and yellow individuals. Multiple radio‐tracked adult males passed through the territory of radio‐tracked adult females during the study. Females of all sizes were more likely to change position each day than males. There were no differences between the sexes or size categories in the distances moved in most months, although the variation in movement distances was higher in the dry season than during the wet season. In the wet season (January–March) movement distances increased and these were size‐ and sex‐related. This increased activity may be associated with mate searching. Males of M. viridis may maximize their rate of encountering mature females by roaming rather than maintaining a home range. Juvenile green pythons moved distances equal to adult snakes in most months despite their comparatively small size.     

Patterns of territory settlement and consequences for breeding success in the Northern Wheatear Oenanthe oenanthe

We examined the pattern of territory settlement and its consequences for breeding success in the Northern Wheatear Oenanthe oenanthe on Bardsey Island, Wales, during the breeding seasons of 1991-93. Males returned earlier than females, and older males returned earlier than first-year breeders. Although their boundaries shifted between years, the general location of territories was consistent during the three-year study. There was a high degree of fidelity to area and territory between years for both sexes. The order of territory settlement, from which a territory rank was calculated, was highly consistent for males between years irrespective of individual settlement patterns and territory fidelity. Patterns of territory settlement were less predictable for females, although there was a significant correlation between the mean territory ranks of paired males and females. There was a male-biased sex ratio in each year, and between 5% and 26% of males remained unpaired throughout the breeding season. Male mating status and breeding success were dependent on arrival date, territory rank and breeding density. Early-arriving, usually older, males were able to settle on territories first and were more likely to pair, while later-arriving individuals were more likely to remain unmated. These effects were consistent between years, and consequently territories could be classified as either preferred (accounting for proportionately more breeding attempts) or non-preferred. Territory quality as opposed to individual quality appeared to explain much of the variation in breeding success, and both sexes benefited by breeding on preferred territories through enhanced breeding success and an increased probability that their offspring would be recruited to the population.     

The courtship and spawning behaviors ofCanthigaster valentini (Tetraodontidae)

Synopsis The sharpnose puffer,Canthigaster valentini, occurs in male-dominated harems of territorial females at Lizard Island (Australia). Spawning occurs daily and year-round. Males only spawn with the females of their social group, inside the female's territory. Females signal their readiness to begin courtship with a display that exposes their egg swollen abdomen. Courtship is long and males do not develop specific courtship colors or perform unique displays. Eggs are fertilized in a demersal nest and there is no parental care.     

The costs of reproduction to males and females of a paternal mouthbrooding cardinalfish Apogon notatus

In the cardinalfish Apogon notatus , starving males mouthbrood the eggs, and females are more active than males in courtship and in attacks against conspecific intruders upon their breeding territory, but sexual ornaments are developed in males. Condition factor, hepatosomatic index and fat body-somatic index declined in both sexes during the breeding season. The deterioration of somatic condition was more severe in females, suggesting that the overall energetic costs were larger for females which produced more than twice as many clutches as males brooded in a season. Selective mortality of females could be due primarily to the depletion of their energy reserves. The increased mortality in females is a possible mechanism for the male-biased operational sex ratio which may provide the potential for sexual selection on males.     

Female-female aggression and female mate choice on black grouse leks

We studied female-female aggression in relation to female mate choice in black grouse, Tetrao tetrix, in central Finland, in 1994-1998. Aggression occurred on average every other minute when there was more than one female on a territory, and aggressive behaviour was most prominent when several females attended the lek. Interactions tended to be proportionally most frequent on the territories of the highest-ranking males, although not significantly so. Females that were chased by other females did not mate with lower-ranking males than their aggressors did. Furthermore, chased females were only rarely (6% of cases) forced to move off the territory by agonistic interactions and copulations were disrupted by other females even less often (3% of cases). The choice of a mating territory did not depend on the outcome of aggression even though the aggressors were more likely to mate on the territory where aggression occurred than elsewhere. There was a marginally significant tendency for aggressors to mate earlier in the season. Females placed themselves further away from other females on the territory when soliciting a copulation than just before aggression. Our results suggest that aggression between females does not effectively constrain female choice in black grouse. Its function may be to aid females to secure undisturbed mating opportunities for themselves rather than to prevent others from mating with a particular male. Copyright 2000 The Association for the Study of Animal Behaviour.     

Differences in fertility and suckling patterns between primiparous and multiparous rhesus mothers (Macaca mulatta)

Primiparous females gave birth around the same time as multiparous nonlactating females, and earlier than did multiparous lactating females. No differences in birth sex ratio were found between primiparous and multiparous females. During the breeding season following birth, primiparous mothers returned to oestrus later than did multiparous mothers, and while few primiparous mothers conceived successfully during that season, most multiparous mothers did. Primiparous females suckled their infants more frequently than did multiparous females at all ages; infants of primiparous females also made more nipple contacts per bout, and had shorter sucking bouts. When mothers came into oestrus, suckling frequency drastically increased for primiparous females, but not for multiparous females, magnifying the differences between the two groups. After the first oestrus, suckling frequency declined for all mothers, but multiparous mothers had consistently lower suckling frequencies than did primiparous mothers. The high suckling frequency, and numerous nipple contacts per bout, found among primiparous mothers are likely to be related to the low reproductive chances that these females faced during the breeding season. Multiparous mothers seemed to compensate for their low suckling frequency by lengthening the suckling bouts, and this suckling pattern did not hinder their reproduction. It is argued that primiparous mothers might have to suckle their infants more frequently because they can only produce milk at slow rates, being in this way forced into a reproductively inhibiting suckling pattern. However, the delay in subsequent reproduction could be ultimately advantageous for primiparous mothers if it enhanced infant survival, and allowed the mothers to regain physical condition before reproducing again.     

Female loggerhead sea turtles (Caretta caretta L.) rarely remate during nesting season

The goal of this study was to assess the consequences of single versus multiple paternity by identifying paternity of clutches per female to identify whether there were detectable costs or benefits. Multiple mating can occur when the benefits of mating outweigh the costs, but if costs and benefits are equal, no pattern is expected. Previous research on loggerhead sea turtle (Caretta caretta) populations found male‐biased breeding sex ratios and multiple mating by many females nesting in southwestern Florida. A sample of nesting loggerhead females who laid more than one nest over the course of the season and a subset of their hatchlings were examined from 36 clutches in 2016 on Sanibel Island, Florida. Males that fathered hatchlings in the first clutch sampled were identified in subsequent clutches. Interestingly, 75% of the females analyzed had mated singly. No male was represented in more than one female's clutches. The results suggest that females likely mate at the beginning of the season and use stored sperm for multiple clutches. Evidence for mating between laying events was limited. There was no consistent pattern across the subsequent multiple paternity clutches, suggesting benefits to loggerhead females likely equal their costs and subsequent mating is likely determined by female preference.     

Breeding territory fidelity in a partial migrant, the American dipper Cinclus mexicanus

American dipper Cinclus mexicanus populations are frequently composed of resident individuals that occupy permanent territories year round and migratory individuals that overwinter with residents but migrate to breeding territories on higher elevation creeks each spring. Between 1999 and 2004 we examined how migratory strategy (resident/migratory) and sex differences influence breeding territory fidelity of American dippers occupying the Chilliwack River watershed, British Columbia, Canada. Counter to expectation we found that the migratory strategy of American dippers did not influence whether birds breeding in one year were found on their former breeding territory in the next. Migratory strategy also did not affect the probability that known surviving dippers occupied the same breeding territory in the following year. Males and females were equally likely to be found on their former territory in the following year (females 43%, males 41%) and known survivors had similar levels of breeding territory fidelity (females 74%, males 68%). However, breeding territory fidelity of males and females varied in response to different factors. Surviving female dippers were more likely to be found on their former breeding territory in the subsequent year following a successful breeding attempt than an unsuccessful breeding attempt. Prior reproductive performance did not influence whether surviving male dippers were found on their former breeding territory. Male dippers were more likely to be found on their former territory and, if they survived, have higher breeding territory fidelity when their mate also returned to that same territory. Mate retention also influenced whether females were found on their former territory in the following year but had no effect on the breeding territory fidelity of known survivors. We argue that sex‐specific dispersal decision rules in American dippers are driven by sex differences in the predictability of breeding performance between years and sex differences in how mate retention influences subsequent reproductive success.     

Long-term territoriality and mate acquisition in the lefteye flounder Engyprosopon grandisquama

Reproductive ecology and function of long-term territoriality in the lefteye flounder Engyprosopon grandisquama were investigated in the southwest of Kyushu Island, Japan. Field observations of marked individuals and monthly sampling suggested that the spawning season was from June to September with a peak in June–July. During the spawning season, males maintained their mating territories, although spawning behavior was not observed in August–September. Some males stayed until the next spawning season and then acquired more mates than newly appearing males, most of which could not acquire mates. Long-term retention of territory may be more advantageous for establishing a mating territory and acquiring mates in the next spawning season.