Being the Winner Is Being the Loser When Playing a Parental Tug-of-War – A New Framework on Stability of Biparental Care

Because there are basic sexual differences in reproductive potential, and the cost of parental care is assumed to be high, biparental care is viewed as a constant tug-of-war between the partners. This raises the question of the system’s evolutionary stability. Several models have been proposed to resolve this problem but none has received unequivocal support. Here, I propose a framework that not only integrates the earlier theoretical ideas (sealed bids, negotiation) but also considers the importance of the environment (frequently neglected in previous models) and views the cost of parental care from a different perspective (costly in terms of parent’s survival only when performed close to the boundary of parental capacity). The framework suggests that sexual conflict may not be such a significant factor mediating parental care as commonly assumed, and that a parent trying to shift the parental burden onto the partner – assumed to be the winner in the tug-of-war interplay – is actually more likely to be a loser, as doing so may put the success of the current breeding attempt in jeopardy, thereby reducing overall fitness of the parent. Once it is realized that the importance of sexual conflict is actually much less than it seems, it becomes clear that the stability of the biparental care system no longer seems to be such a puzzling issue.

Breeding biology of two sympatric Nesospiza finches at Nightingale Island, Tristan da Cunha

Nesospiza finches are a classic example of a simple adaptive radiation, with two ecologically distinct forms confined to the Tristan da Cunha Archipelago, South Atlantic Ocean: an abundant, small-billed dietary generalist, and a scarce, large-billed specialist. These have segregated into two species at Nightingale Island, but there is still local introgression between the two forms at Inaccessible Island. We describe the phenology and breeding behaviour of the two sympatric species at Nightingale Island (2.6 km2): Wilkins’s Finch Nesospiza wilkinsi (Endangered) and Nightingale Island Finch N. questi (Vulnerable). The finch breeding season starts in late October-November but the onset of breeding varies by 4–5 weeks among years. The small-billed Nightingale Island Finch typically (two of three study seasons) starts breeding 1–3 weeks earlier than the large-billed Wilkins’s Finch, unlike at Inaccessible Island where the Wilkins’s Finches start breeding first. Laying of initial clutches was quite well synchronised, peaking 1–2 weeks after the first nests were found. Females constructed the nests, which were mostly (>90%) in dense Spartina arundinacea tussock grass stands and occasionally in ferns or sedge grasses. Clutches comprised one or two eggs, with no difference between Wilkins’s (1.66 ± 0.48) or Nightingale Island finch clutches (1.71 ± 0.46). Incubation periods averaged longer for Wilkins’s Finch (18.3 ± 0.5 d) than Nightingale Island Finch (17.7 ± 0.5 d), but this difference was not statistically significant. Females incubated the eggs, and were fed by the males. The difference in egg volume within two-egg clutches was 2–13% for Wilkins’s Finches (mean 5.9 ± 3.3%) and 1–19% for Nightingale Island Finches (mean 8.4 ± 5.3%). At least 31% of pairs re -laid after their first breeding attempt failed but there was no evidence of double brooding. Repeat nests were 0–20 m (mean 5.6 ± 4.9 m) from the initial nest site and inter-seasonal nest sites for 38 known pairs were 0–33 m apart (mean 12 ± 9 m). No inter-species pairs or hybrid birds were seen, but two instances of inter-species fledgling provisioning were observed.

New Clone of Sesenduk (FRIMsrp001)

The clone was produced from a breeding attempt on pioneer indigenous species of Endospermum diadenum. Seeds from the tree were collected and then were propagate and germinated in FRIM’s nursery. The selection process continued for the progeny which has possessed vigorous growth among others. A bud from the plant was successfully tissue-cultured, which multiplied and developed roots in glass container. The clone was planted in year 1996 at Kepong Botanical Garden (FRIM’s KBG) and Kampung Jawa plantation plots in FRIM. The seedlings of the clone were able to grow and survive at open site. Several trees of the planted clone from these areas have been cut for timber testing for its basic properties as well as for product development. The wood of the clone trees possessed good physical and mechanical properties and acceptable wood colour (yellow to white colour). The trees were able to achieve 30cm in diameter and 24m in height of straight bole in 10 years after planting provided that the soil at the plantation site is well-nurtured. Short rotation of planting, practiced for the clone is suitable for forest plantation and sustainable supply of raw material either for solid furniture industry or wood-based industry.

An integrative measure of cognitive performance, but not individual task performance, is linked to male reproductive output in budgerigars

Cognitive abilities such as learning and memory are key for survival and reproduction. Individuals with high cognitive abilities may be more successful at attracting mates and producing offspring. However, empirical tests of and evidence supporting this hypothesis remain scarce. We measured cognitive performance of male budgerigars in four tasks: problem solving, detour reaching, seed discrimination, and spatial memory. We then tested female choice for male cognition at three stages of the mating choice process: social pairing, extra-pair mating, and continued reproductive investment with a social mate. We also measured female reproductive output. We used an integrative measure of male cognitive performance that encapsulates performance across all tasks, the ‘composite cognitive score’ by summing performance on the four tasks. In the first stage, females did not choose their social mates based on any of the measures of male cognitive performance. In the second stage, however, males with higher composite cognitive scores sired and raised more offspring. In the third stage, females increased their reproductive investment after the first breeding attempt when paired with males with higher detour-reaching scores. These results suggest that female reproductive decisions may shape overall male cognitive performance.

Incubation Onset Influences Maternal Investment in Eggs and Egg and Nestling Survival in an Altricial Bird

Many birds initiate incubation before clutch completion which results in asymmetric survival of eggs and nestlings within the clutch. When parents start incubating before clutch completion, low survival is expected of the nestlings hatched from eggs laid after the onset of incubation due to hatching asynchrony. Conversely, eggs laid before the onset of incubation may have a lower survival because of extrinsic factors (e.g. ambient temperature and microbial infection). Many studies investigating the allocation of parental investment have hypothesized two different strategies wherein parents allocate investment that favors eggs/nestlings with high survival prospects or compensates for the disadvantages of eggs/nestlings with low survival prospects. Although birds could take different strategies based on incubation onset within the same breeding attempt, this idea has never been tested. We conducted an observational study to investigate the effects of incubation onset on the survival of eggs laid before and after incubation onset and parental egg allocation in the altricial wryneck Jynx torquilla. We found that survival decreased in the eggs laid earlier or later than the day of incubation onset within the clutch. Because egg volume increased with laying sequence, egg volume and the survival of eggs laid before incubation onset were positively associated, whereas egg volume and the survival of eggs laid after incubation onset were negatively associated. Furthermore, late-hatching nestlings grew to similar weights to early-hatching nestlings. These suggest that females proportionately invested in egg size before incubation onset, but that investment in egg size after incubation onset was compensatory. Our observational study proposes a possibility that female wrynecks adopt two different investment strategies before and after incubation onset during a breeding attempt.

Copying nesting attempts in a new site may be the wrong choice. A case in the European Bee-eater (Merops apiaster)

Insistent nesting attempts by a group of European Beeeaters in a new site, a pebbly bank of the middle course of Trebbia River, northern Italy, mostly failed because of the unmovable pebbles encountered during tunnel excavation. The birds later nested in an artificial sand heap, with full success that time. Various considerations suggest that birds insisted in the unsuitable site because they copied the nesting activity of model conspecifics. Finding social attraction and “public information” from conspecifics in a place where no breeding attempt was previously made would allow disentangling social philopatry from spatial philopatry.

Investigating sex differences in genetic relatedness in great-tailed grackles in Tempe, Arizona to infer potential sex biases in dispersal

In most bird species, females disperse prior to their first breeding attempt, while males remain closer to the place they hatched for their entire lives. Explanations for such female bias in natal dispersal have focused on the resource-defense based monogamous mating system that is prevalent in most birds. In this system, males are argued to benefit from philopatry because knowing the local environment can help them to establish territories to attract females, while females are argued to benefit from dispersing because they can find suitable unrelated mates. However, theoretical, field, and comparative studies highlight that the factors shaping dispersal decisions are often more complex. Studying species with different social and mating systems can help illuminate the relative role of various factors in the evolution of sex biased dispersal. Here, we use genetic approaches to determine whether females and/or males disperse in great-tailed grackles (*Quiscalus mexicanus*), which have a mating system where the males hold breeding territories that multiple females might choose to place their nest in, but females forage independently of these breeding territories across a wider area. First, we find that, for individuals caught at a single site in Arizona, the average relatedness among all female dyads is higher than expected at random, whereas average relatedness among all males dyads is not. Second, we find that female close relatives are found within shorter distances from each other than pairs of unrelated females, whereas male close relatives are found at larger distances from each other than pairs of unrelated males. Third, we find a decline in relatedness with increasing spatial distances for females, but not for males. These relatedness results suggest that, unlike most other bird species, female great-tailed grackles appear to have hatched and remained at this site, while males disperse to new areas. Our findings show that great-tailed grackles offer a relevant study system to further understand the factors shaping natal philopatry and dispersal, given this reversal of the usual sex-bias in dispersal together with their divergent social and mating system.

Daurian redstart Phoenicurus auroreus is a host for the common cuckoo Cuculus canorus during the second, but not the first cultch

Background: Coevolution in cavity-nesting host-cuckoo systems may differ from those in open-nesting hosts due to unique conditions in cavity nests. We investigated brood parasitism in Daurian redstarts ( Phoenicurus auroreus ), a regular cavity-nesting host of common cuckoos ( Cuculus canorus ).Results: A total of 15.6% ( n =358) of host nests were parasitized by cuckoos. Cuckoos were highly successful in parasitizing Daurian redstart nests: nearly all cuckoo eggs were laid in the nest cup, and all cuckoo chicks evicted all host offspring. However, egg ejection by Daurian redstarts was egg morph specific, i.e. hosts laying white eggs ejected most real cuckoo eggs, while hosts laying blue eggs did not eject any. In contrast, hosts ejected most mimetic cuckoo eggs. Moreover, most Daurian redstarts moved to nearby villages during the second breeding attempts, where the risk of cuckoo parasitism was reduced. Parasitism only occurred during the second breeding attempt, since cuckoos had not yet arrived at the breeding grounds when hosts started to lay their first clutches, which may indicate a novel and unique anti-parasite defense, advancing breeding time of hosts.Conclusions: Our results suggest that Daurian redstarts suffer from high risk of cuckoo parasitism showing more intense egg ejection while building nests closer to human habitation in the second clutch. This suggests that cavity-nesting hosts may show adaptations to brood parasites that differ from those of open-nesting hosts.

Maternity uncertainty in cobreeding beetles: females lay more and larger eggs and provide less care

Cobreeding, which occurs when multiple females breed together, is likely to be associated with uncertainty over maternity of offspring in a joint brood, preventing females from directing resources towards their own offspring. Cobreeding females may respond to such uncertainty by shifting their investment towards the stages of offspring development when they are certain of maternity and away from those stages where uncertainty is greater. Here we examined how uncertainty of maternity influences investment decisions of cobreeding females by comparing cobreeding females and females breeding alone in the burying beetle, Nicrophorus vespilloides. In this species, females sometimes breed together on a single carcass but females cannot recognize their own offspring. We found that cobreeding females shifted investment towards the egg stage of offspring development by laying more and larger eggs than females breeding alone. Furthermore, cobreeding females reduced their investment to post-hatching care of larvae by spending less time providing care than females breeding alone. We show that females respond to the presence of another female by shifting allocation towards egg laying and away from post-hatching care, thereby directing resources to their own offspring. Our results demonstrate that responses to parentage uncertainty are not restricted to males, but that, unlike males, females respond by shifting their investment to different components of reproduction within a single breeding attempt. Such flexibility may allow females to cope with maternity uncertainly as well as a variety of other social or physical challenges.

Making the best of a bad job? Chick mortality and flexible female brood care in Snowy Plovers

Offspring desertion represents a trade-off between current and future reproductive success. Its timing is crucial as the termination of parental care has profound consequences for the fitness of the parents and their offspring. However, the decision process involved with termination of care is still poorly understood. Snowy Plovers Charadrius nivosus show highly flexible brood care with females either deserting the brood early or providing care for an extended period. Deserting females often quickly remate and start a new breeding attempt. Using a dynamic modelling framework, we investigated the decision-making process for continuation or termination of care by females over a seven-year period. The length of female care increased over the season likely reflecting lower re-mating opportunities for deserting females late in the season. Present brood size, assessed daily during the brood care period, was strongly related to the length of female care: females were more likely to stay and care for larger than for smaller broods. Chick death and desertion frequently coincided, suggesting that poor offspring condition served as a trigger for female desertion. Overall, deserting females had a similar number of fledglings to caring females. This suggests that for many females, desertion was not a strategy to escape the shackles of monogamy and secure higher reproductive success through sequential polygamy. Rather, most deserting females made the best of a bad job when conditions were poor and their continued presence did not make a difference for the survival of their young. We conclude that when making the decision to continue or terminate care, Snowy Plover females monitor the condition of their offspring closely and adjust their care flexibly to the value and needs of their young.