Factors affecting the duration of nest defense and reproductive lifespan of female sockeye salmon, Oncorhynchus nerka

Reproductive success of female animals is often affected by a combination of fecundity and parental care. In female salmonid fishes, acquisition of nest (redd) sites and prevention of their use by other females are critical to reproductive success. These factors are particularly important for stocks that spawn at high densities. Body size is positively correlated with fecundity and egg size, and has been hypothesized to control the outcome of intrasexual competition and longevity. We tested this hypothesis by evaluating the influences of body size, intrasexual aggression and arrival date on duration and success of redd guarding by female sockeye salmon, Oncorhynchus nerka, in a small Alaskan creek. Contrary to the hypothesis, larger females guarded their redds no longer than smaller females, and did not live as long in the stream. Aggression was not related to body size or overall longevity but was positively correlated with residence period on the redd. Females that entered the creek earlier lived longer, spent longer on their redds, and spent more time guarding their redds after spawning than females that entered the creek later. However, despite their longevity, early-arriving fish were more likely to have their redds reused by another female because they died before all the females had selected redd sites. The small average body size in this stock is consistent with weak selection for large size, and with our evidence that size provided little if any advantage in nest guarding.     

Parental investment of male two-spotted goby, Gobiusculus flavescens (Fabricius)

The trade-off between parental care and feeding was studied in the male two-spotted goby (Gobiusculus flavescens F.). Two temperatures, 8.5 degrees C and 13.0 degrees C, were used, with five replicates at each temperature, in order to determine whether temperature influenced parental behaviour. In each replicate, two males and four females were introduced to an aquarium, where the males chose between two nests and courted the females. In each replicate, one male spawned. After spawning, the males guarded the eggs until hatching. The guarding males' behaviour was recorded with a video camera twice a day (15 min each time), once before and once after they were fed. The male's condition (c-factor) was calculated at the start of the experiment and after egg hatching. The eggs were spawned in an artificial nest (half of a PVC tube), and attached to the nest in a single layer. The areas with eggs (representing brood size) were marked after spawning and the fry counted after hatching (which was used to calculate area hatched). Numbers of prey eaten (plankton) and number of aggressive encounters between the guarding male and the other fishes were recorded. Time spent in the nest and time used on fertilisation, fanning and cleaning were estimated and related to egg age, brood size, hatching success, temperature and food availability (no food or food).The results showed that feeding (expected to influence future reproduction) decreased and parental expenditure (current reproduction) increased, as the eggs developed (became closer to independence). Parental expenditure was significantly higher at 13.0 degrees C than at 8.5 degrees C, presumably due to higher oxygen demands by the eggs, and a greater risk of egg-infections. The c-factor of the males guarding eggs decreased over time, in contrast to the non-guarding males' c-factor. Guarding males' aggressiveness decreased as the eggs got older, but increased just before hatching. A possible explanation for this could be the decreasing intrusion by the non-guarding male and females caused by high aggressive behaviour by the guarding male early in the brood cycle. The exploitation of the nest (percentage of total nest area covered by eggs) seemed to determine the amount of parental expenditure and loss of condition, while brood size (area of eggs) had no effect.     

Female mate choice,male-male competition and parental care in the river bullhead,Cottus gobio L. (Pisces,Cottidae)

Male body size was tested for its influence on female mate choice, male-male competition and ability to defend broods in the river bullhead, Cottus gobio L., a polygynous fish with paternal care. Females presented with two potential mates of different sizes significantly preferred to spawn with the larger male. Males smaller than, or 1·5 times longer than, the female were rarely selected as mates. Larger males were more successful in defending their brood from conspecifics, which may explain female preference for them. Unmated large males displaced smaller guarding males from their nests and retained the acquired egg masses. Competition between males for nest sites with eggs can be accounted for by the preference of females for males already guarding eggs: by seizing a nest containing egg masses, a male will increase his chance of being chosen.     

Have your cake and eat it too: male sand gobies show more parental care in the presence of female partners

Traditionally, male parental effort and mate attraction effortare expected to be in conflict as they compete for the sameresource budget. However, the quality of care provided by themale may be of a direct benefit to females and may provide animportant mate choice cue. In a laboratory experiment, we examinedhow males modified their parental behavior with respect to matingopportunity by allowing male sand gobies to mate with a singlefemale either in a big or small nest (a constraint on futuremating potential). We then exposed half of these males to thevisual stimulus from additional females and recorded male eggfanning and nest building (two components of care), courtshipbehavior, and reproductive success through out the brood cycle.We found that males fanned longer and more frequently and didmore nest construction in the presence of females and in bignests. Males guarding large nests courted females more thandid males guarding small nests. All males consumed eggs duringthe brood cycle, but complete clutch cannibalism was most frequentwhen males were guarding small nests in the absence of females.The pattern of filial cannibalism that we observed suggeststhat males prematurely terminated care when their reproductivepotential was low, that is, when there was little nest spacefor additional mating and no mates present. We found no supportfor a trade-off between mate attraction and parental care. Indeed,taken together our results suggest that males may use parentalcare as a courtship strategy and that males who invest in mateattraction also have higher parental effort.     

Parasites and parental care in male upland bullies (Eleotridae)

Parental care of eggs by male upland bullies Gobiomorphus breviceps was studied in the field and in the laboratory, with special emphasis on the effect of infection by trematode cysts. In the field, the proportion of old eggs in the nest affected the time taken by males to return to their nest after being chased away, but only in one year of the study. No effects of male size, male parasite load, number of eggs per nest or nest characteristics were observed. In the laboratory, heavily-infected males spent more time fanning their eggs than lightly-infected ones. Smaller males also tended to spend more time fanning than large males. Male size, parasite load and number of eggs per nest had no measurable effect on the aggressiveness of guarding males towards intruders, weight loss in males or egg incubation time. Parental investments did not vary as a function of age of the eggs. All males cannibalized some of their eggs, and there appeared to be a threshold brood size below which males consumed their entire brood. Overall, results were not consistent with those of studies on other fish species, and indicate that rules of investment in parental care may be different for fish inhabiting harsh, unpredictable environments.     

Antimicrobial egg cleaning by the fringed darter (Perciformes: Percidae: Etheostoma crossopterum): implications of a novel component of parental care in fishes

Broad-spectrum antimicrobial compounds have recently been identified in the epidermal mucus of fishes and probably serve as a first line of defence against microbial pathogens. Because of the ubiquitous nature of fungi and bacteria in aquatic systems, defence against these pathogens should be required throughout the lifespan of fishes, including the egg stage. We conducted experiments on Etheostoma crossopterum (Percidae: Catonotus), the fringed darter, to determine if the presence of a guarding male inhibits microbial colonization of eggs. Based on results from a combination of in-stream experiments, in vitro microbial assays, and morphological characteristics and behaviour of breeding males, we propose that antimicrobial egg cleaning by the guarding male is an effective component of parental care in these fish. Although innate antimicrobial compounds have been identified in a variety of organisms ranging from insects to vertebrates, integration of these compounds into a species's reproductive life history has been identified only in a small number of insect species. The results from this study not only indicate that E. crossopterum males provide a novel form of vertebrate parental care, but also have implications regarding the evolution of parental care in fishes and transitional evolutionary stages from no parental care to male parental care.     

Male mating success and female mate choice in the river sculpin,Cottus nozawae (Cottidae)

Synopsis Mating success of males and its correlates were investigated in a natural population of the polygynous fluvial sculpinCottus nozawae. Furthermore, the female mate preference of this species was examined experimentally under alternative conditions for mating in a stream. The mating success of individual males (the number of females with which a male mated) ranged between 0 and 8 with a mean of 2.41 in 1983 and 2.52 in 1989, in a population of which the sex ratio was about 1 : 2 in both years, skewed toward females. Mainly due to the excess of nests without egg masses and the few nests with one egg mass, the distribution of male mating success did not fit a Poisson distribution, indicating its non-randomness. Male mating success was not correlated either with the size of the nest rocks or with the male size, suggesting that these two variables are not determinants of mating success. The mate choice experiments demonstrated that females of this species more frequently chose smaller males as mates whose nests already contained eggs than large males without eggs. Additionally, an analysis of stomach contents of guarding males suggested that the parental males ate their own eggs during egg guarding (filial-cannibalism). Based on these results and on a comparison of reproductive characteristics with congeneric species, it is suggested that one of the most important determinants for female mate choice inCottus species may be whether or not parental males are filial egg cannibals.     

Sex-specific defence behaviour against brood parasitism in a host with female-only incubation

Nest protection against intruders is an indispensable component of avian parental care. In species with biparental care, both mates should evolve nest defence behaviour to increase their reproductive success. In most host-parasite systems, host females are predicted to have more important roles in nest defence against brood parasites, because they typically are primarily responsible for clutch incubation. Male antiparasitic behaviour, on the other hand, is often underestimated or even not considered at all. Here we investigated sex-specific roles in four aspects of great reed warbler (Acrocephalus arundinaceus) nest defence against a brood parasite—the cuckoo (Cuculus canorus), namely (1) mobbing, (2) nest attendance/guarding, (3) nest checking and (4) egg ejection. Using dummy experiments, simulating brood parasitism and by video-monitoring of host nests we found that males took the key roles in cuckoo mobbing and nest guarding, while females were responsible for nest checking and egg ejection behaviours. Such partitioning of parental roles may provide a comprehensive clutch protection against brood parasitism.     

Reproductive success in male sunbleak, a recent invasive fish species in the U.K.

The spawning behaviour of male nest guarding sunbleak Leucaspius delineatus , a recent invasive species in southern England, was studied and quantified for the first time. In the absence of physical differences between territorial and non‐territorial males ( i.e . colour, size, etc .), the reproductive behaviour of territorial males was analysed and related to reproductive success. The results showed that females preferred high‐courting and highly aggressive males. The initial cue in female mate choice, however, was based on courtship, while aggression was the decisive behavioural trait in influencing mate choice, providing a direct signal of physical condition and 'paternal competence'. Some males picked nest sites which were subsequently preferred by other males taking over the nest of a previous male ('communal nest'), with the new territorial male adopting the eggs already present at the nest. It appears that either due to female preference for nests already containing eggs or lower rates of sired egg predation by dilution among unrelated eggs, sunbleak males have adopted the mating strategy of allopaternal care.     

Large males have a mating advantage in a species of darter with smaller, allopaternal males Etheostoma olmstedi

Theory suggests that males that are larger than their competitors may have increased mating success, due to both greater competitive ability and increased attractiveness to females. We examined how male mating success varies with male size in the tessellated darter Etheostoma olmstedi. Previous work has shown that large males tend to move around and breed in vacant breeding sites, and consequently provide less care for their eggs, while smaller individuals can be allopaternal, caring for the eggs of other males as well as for their own. We studied female egg deposition in a natural breeding population using artificial breeding sites and in the laboratory, where female choice of spawning site was restricted to two breeding sites tended by two males of different sizes. In both the field and the laboratory, nests tended by larger males were more likely to receive new eggs. Additionally, the mean size of males associated with a nest was positively correlated with both the maximum coverage of eggs at the nest and the number of times new eggs were deposited. We discuss how the increased mating success of larger males, despite their decreased parental care, may help explain allopaternal care in this species [Current Zoology 56 (1): 1-5, 2010].     

Why egg-caring males of Isaza (<Emphasis Type="Italic">Gymnogobius isaza</Emphasis>, Gobiidae) refuse additional females: preliminary field observations

Like many other gobies, males of the Isaza goby, Gymnogobius isaza endemic to Lake Biwa, Japan, conduct parental care of eggs at nests, and females are likely to choose mates while visiting nests. The reproductive strategy should induce polygyny, but Isaza males never accept additional females in one breeding cycle. Sampling data of broods indicated that the egg mass areas were much smaller than the nest sizes, suggesting that nest size is not the limiting factor in obtaining further eggs from additional females. The brood size greatly decreased as the duration of care progressed. Few individuals including caring males ate eggs, and heterospecific egg predators were rarely observed. Sixty percent of egg masses at the middle stages of egg development were infected with aquatic fungi, some being covered with a fungus mat that drastically reduced survivorship. Infected egg masses contained more eggs than non-infected ones at the same stage, indicating that large egg masses are prone to be frequently destroyed by fungi. It is likely that the activity of parental males is lowered during the long care periods at low water temperature in early spring. Such lowered activity of caring males might be responsible for infections in large broods that would have needed more care. We propose the hypothesis that male rejection of additional females may be related to optimal brood size, which will be less susceptible to fungus infection and produce more hatching young than otherwise. This hypothesis will explain not only male avoidance of additional females but also some unique reproductive behaviors of this fish such as some females spawning of a portion of of the mature eggs in one nest.     

Paternity, parental behavior and circulating steroid hormone concentrations in nest-tending male bluegill

Like many teleost fishes, bluegill (Lepomis macrochirus) are characterized by sole male parental care of offspring. In addition, bluegill parental males experience cuckoldry by specialized parasitic male morphs. This cuckoldry has previously been shown to influence the expression of parental care behavior. To better understand some of the proximate mechanisms mediating parental behavior, we examined the relationships between circulating steroid hormones, paternity, and parental behavior during the egg and fry stages of care in parentals that spawned during the first third of the breeding season. During the egg stage of care, we found that males with higher paternity had lower levels of testosterone, but there was no relationship between paternity and either 11-ketotestosterone or cortisol. There also was no relationship between the hormones and care behavior comprising fanning of the eggs, nest rim circles, chases of brood predators, or pecking at the eggs (indicative of egg cannibalism), except for a negative relationship between cortisol and pecking behavior. During the fry stage of care, we conversely found that males with higher paternity had higher levels of testosterone and 11-ketotestosterone. There also was a negative relationship between the concentrations of these two androgens and the defensive behavior of males when exposed to a potential brood predator (a pumpkinseed, Lepomis gibbosus). We discuss these results in relation to previous work in fishes and other vertebrate taxa. Overall, our data suggest a complex relationship between circulating steroid hormone levels, paternity and parental behavior.     

Male body size and brooding success under natural conditions in the freshwater Japanese goby, Rhinogobius sp. OR (orange type)

Males of the Japanese goby Rhinogobius sp. OR (orange type) establish nests under stones in streams. They provide care to egg masses until hatching. We carried out field observations and a field experiment in a natural stream to examine the effect of male body size on brooding success. An experiment excluding guarding males indicated that their presence has a positive effect on nest defense. Field data showed that male body size was positively correlated with the size of the egg mass that was initially found at the nest. Furthermore, a sequential increase in egg mass size seen in the nests of larger males indicated that multiple females spawned during a single breeding cycle of larger males. To examine male brooding success, two dependent variables, egg mass persistence (days from initial egg mass to disappearance or hatching) and hatching success were analyzed. The results indicated that the variation found in both dependent variables was significantly explained by two independent variables, namely, initial egg-mass size and the number of matings. It is also suggested that male body size indirectly influenced brooding success through positive correlations with these independent variables.     

Costs of egg caring in the skink, Mabuya longicaudata

Why do most animal species not provide parental care to their eggs or progeny? The “cost” hypothesis suggests that parental care can reduce food intake, probable survivorship, and/or subsequent fecundity of the reproductive female, and parental care is not adaptive unless it is balanced by considerable fitness trade-offs. Therefore, parental care would be expected to evolve most often in species in which such costs are minor or insignificant. Although parental care has been reported in more than 140 species of reptiles, few records unambiguously demonstrate the cost of parental care. In the current study, I report the “costs” of maternal activities and survivorship, as well as egg attendance times, and within- and between-seasonal body size variations, of females of Mabuya longicaudata after engaging in parental care. I used those data to test whether parental care necessarily entailed large costs to mother lizards. The proportion of nests guarded decreased with time after eggs were laid, with most females remaining at the nest for at least 1 week, but then some beginning to leave. The loss of mass by females over the first week of egg guarding was on average balanced by a gain in mass during subsequent foraging bouts. The snout–vent length (SVL), body mass (BM), recapture (survival) rates, fecundity, timing of a second clutch, and clutch frequencies of females that exhibited long-term parental care (more than 28 days; mean, 31.6 ± 2.2 days) did not significantly differ from that of females that showed short-term parental care (9～16 days; mean, 12.5 ± 2.3 days). Thus, my data indicate that intense parental care over a long period does not necessarily entail major energy costs for the mother in terms of SVL, BM, recapture (survival) rates, or fecundity.     

Circulating androgens are influenced by parental nest defense in a wild teleost fish

While social interactions influence vertebrate endocrine regulation, the dynamics of regulation in relation to specific behaviors have not been clearly elucidated. In the current study, we investigated whether androgens (testosterone) or glucocorticoids (cortisol) play a functional role in aggressive offspring defense behavior in wild smallmouth bass (Micropterus dolomieu), a teleost fish with sole paternal care. We measured circulating testosterone and cortisol concentrations in plasma samples taken from parental males following a simulated nest intrusion by a common nest predator, the bluegill sunfish (Lepomis macrochirus). To understand whether endocrine regulation changes across the parental care period, we looked both at males guarding fresh eggs and at males guarding hatched embryos. Plasma testosterone levels increased in males subjected to a simulated nest intrusion when compared to sham controls. Testosterone concentrations in males guarding embryos were lower than in males guarding fresh eggs, but circulating testosterone was positively correlated with the level of aggression towards the nest predator at both offspring development stages. However, there was no increase in cortisol levels following a simulated nest intrusion, and no relationship between cortisol and any measured parameter. These results suggest that androgens play an important role in promoting aggressive nest defense behavior in teleost fish.     

Determinants of male mating success in a natural population of a stream goby of the genus Rhinogobius

The mating success of individually identified males of a stream goby, Rhinogobius sp. CB (cross‐band type), was recorded over one breeding season. One to 3 year‐old males were active in mating, but 3 year‐old males, which accounted for 36% of the population, amounted to c . 70% of the total males guarding eggs in the nest. Three quarters of the breeding males had only one brooding cycle, but the others had two or three. All the latter males changed their nest sites between cycles within a riffle. In 1 and 2 year‐old males, the number of brooding cycles contributed more to the mating success than egg mass size in one brooding cycle. For mating success of 3 year‐old males, the egg mass size in one brooding cycle, which can be enhanced by spawning with a large female or multiple females, was as important as the number of brooding cycles. These male reproductive tactics could be attributed to the age‐related ability of nest construction and mate acquisition.     

Mate choice and cannibalism in a natural population of a stream goby,Rhinogobius sp.

Breeding ecology of the stream goby,Rhinogobius sp. LD (Large Dark), was investigated under natural conditions. Males selectively courted females of similar size to lead them to the nests, whereas females followed courting males preferentially when the relative male size was greater. Male-male competition for a female was relatively infrequent and not severe. Developmental stages of eggs and egg numbers in one nest indicated that males receive 1–3 clutches during one breeding cycle. Males guarding multiple clutches frequently ate some of the eggs, but those guarding single clutches rarely did so. Gravid females in the nest also frequently cannibalized eggs laid by a previous female, probably in order to extend the area available for egg deposition. Mate choice in this species is discussed in relation to paternal ability, limitation of available spawning area and the female-biased sex ratio.     

Parental care and mating systems of cichlid fishes in Lake Tanganyika: a preliminary field survey

Reproductive ecology and ethology of 52 cichlid fishes were studied along the shore of Myako, east-middle coast of Lake Tanganyika. Seventeen species were substrate-brooders (guarders), 31 were mouthbrooders, and the remaining 4 were intermediate, performing prolonged biparental guarding of fry after mouthbrooding. Among the substrate-brooders maternal care (and polygyny) was seen about as frequently as biparental care. In most of the mouthbrooders only females took care of the brood, but in 3 species eggs and small larvae were mouthbrooded by females and larger fry by males. In most of the maternal mouthbrooders males defended mating territories which females visited to spawn. The mating system differed from lekking in that there was no concentration of territories and males fed within them. In the remaining maternal mouthbrooders males and overlapping home ranges and only temporarily defended courtship sites in each bout of spawning. Brood size, egg size, breeding site, and sexual differences in body size and color are described. The relationship between parentalcare patterns and mating systems within the family Cichlidae are discussed.     

Male parental care and its adaptive significance in a neotropical frog

In the Puerto Rican frog Eleutherodactylus coqui, parental care is performed exclusively by males, and consists of attending the eggs and hatchlings at a terrestrial oviposition site. The two major behavioural components of parental care are egg brooding and nest defence against conspecific egg cannibals. Defence behaviour includes aggressive calling, biting, sustained biting, wrestling, and blocking directed against nest intruders. Parental care lasts from oviposition to hatching (17–26 days) and often for several days after hatching. During pre-hatching development, males are present in their nests 97.4% of the time during the day and 75.8% of the time at night. A large portion of this time is spent brooding eggs. In a field experiment, males were removed from their nests and the fate of clutches was monitored. Compared to control clutches (males not removed), experimental clutches had significantly lower hatching success and suffered significantly greater mortality from desiccation and cannibalism. Hence, parental care yields significant benefits to male fitness via increased offspring survival.