Jeffrey R. Baylis

The evolution of parental care in fishes, with reference to Darwin's rule of male sexual selection

SynopsisA simple two part hypothesis is proposed to describe the sources of selection influencing the evolution of parental care in fishes. It is derived in part from the observation that most fishes exhibiting complex patterns of parental behavior are freshwater forms. The first aspect of the hypothesis assumes that differential zygote mortality occurs in spatially and temporally varying environments. The second assumes that rates of gametogenesis are faster in males than in females. These aspects interact to generate a series of predictions: 1. When the zygote requires an external resource such as an optimal site for development, and that resource is scarce relative to the breeding population and is reusable, the male should monopolize it (male reproductive territoriality). 2. When bearing is derived from male guarding, the male will be the bearer. 3. When bearing evolves from a condition other than male guarding, the female will be favored as the bearer and the male will be favored as the gamete donor. 4. In all of the above cases except male bearing, the males reproductive success is limited primarily by the number of females he can attract rather than his own rate of gamete production and hence the male will tend to be the sexually selected sex. These and other predictions are tested against the existing literature on reproduction in fishes, and competing hypotheses are critically reviewed.

Male body size and paternal behaviour in smallmouth bass, Micropterus dolomieui (Pisces: Centrarchidae)

Male smallmouth bass defend nest sites and progeny after spawning. Females may consequently discriminate between potential mates with respect to characters that indicate paternal quality. Survivorship of offspring was previously found to be positively related to the site tenacity of a male following a disturbance at the nest. In this study, a comparison of the behaviour of 462 males over four spawning seasons indicated that both body size and the developmental stage of offspring in nests influenced male guarding behaviour. Large males were more site-tenacious than small males following a human disturbance at the nest, but the strength of the association differed between spawning seasons. Males that were guarding eggs at the time of intrusion were more tenacious than males that were guarding larvae, suggesting the higher ventilation requirements of eggs may motivate males to assume higher risks of injury. Male tenacity depended neither on the date of the spawning season on which male behaviour was evaluated, male age, nor the number of offspring defended after accounting for male body size and the developmental stage of offspring. Male body size could thus provide female M. dolomieui with an a priori indicator of the paternal quality of potential mates. Comparisons of male mortality indicated that the cost of reproduction did not depend on body size and that large parental males suffered a higher reproduction-independent mortality than small parental males. Size-dependent mortality could consequently favour a relatively higher investment into current progeny by large males. Large males should also be capable of a higher absolute investment into current offspring than small males because of size-dependent metabolism and reduced feeding during the period of parental care. Higher absolute investment by large males may explain the apparent female mate preference for large male M. dolomieui and the tendency for females to prefer large males as mates in other fishes with paternal care.

Complete Estimates of Repreductive Success in a Closed Population of Smallmouth Bass (Micropterus Dolomieui)

We conducted a 4—yr study of 154 parental male smallmouth bass (Micropterus dolemieui) and 982 nests in a closed natural population (a temperate seepage lake in Wisconsin). Our goal was to test common assumptions and hypothesis about reproduction in natural populations. Mark—recapture techniques were used to measure changes in the demography, age—specific sex ratios, and mortality rates of the whole population. An area—density method was used to estimate the number of eggs spawned in each sampled maless nest, and we volumetrically estimated the number of larvae produced by sampled males. The lake is closed to migration, allowing us to accurately estimate total population size and individual variance in reproductive success (RS) for each year without having to assume a demographically stable population. We found that a large proportion of non—breeding adults of both sexes were present in each year. We compared estimates of variance in RS among subsets of males and females in the population to examine the effect on variance when mature non—breeding individuals are included in the analysis. Excluding non—breeders resulted in the true variation in RS being underestimated and the mean RS overestimated, both by a factor of °3 for males and 2 for females. Most male bass spawned only once in their lifetimes, and size at age 3 yr appeared to determine whether a male spawned or postponed reproduction. Males that bred at age 3 yr were among the largest of their cohorts, and males that bred at age 5 yr were among the slowest growing. There may be greater selection on adults for opportunity to breed than there is selection in RS among breeding adults in this population.

Alternating Life Histories of Smallmouth Bass

Abstract We review some patterns of reproduction among and within cohorts of male smallmouth bass Micropterus dolomieu in Nebish Lake, Wisconsin. Previous studies of the population have shown that many males and females fail to breed in a given season and that males are effectively semelparous. Age at first reproduction among males of a cohort appears to be mediated by size, which may in part explain the large number of males failing to breed in a given year. We suggest that competition among cohorts of males result in older males breeding earlier within a season than younger males and that differences in reproductive timing within a season ultimately determine the age at which males of the next generation reproduce. We argue that the observed differences in age at reproduction among males are not alternative life histories, but are the result of a single alternating life history pattern in which males breeding at a young age produce male offspring that breed at an old age and vice versa. The evolution of...

MALE FITNESS, BODY SIZE AND TIMING OF REPRODUCTION IN SMALLMOUTH BASS, MICROPTERUS DOLOMIEUI

We conducted a mark-recapture study and a survey of nesting male small- mouth bass, Micropterus dolomieui, to determine the relationship between age at first reproduction and fitness among males of several cohorts. Males that spawned at 3 yr of age obtained on average many more eggs than males that delayed reproduction, suggesting that age at reproduction is a conditional strategy. Body size appears to be the trait used to determine the value of the life history decision; small age-3 males were more likely to delay reproduction than large males. The tactic adopted by males may also depend on events that occur well before the time of the life history decision, as males of a cohort that were large at age 3 were also large at age 1. Furthermore, growth over that time period was depensatory. Thus, environmental influences during early ontogeny could potentially direct males into alternative life history pathways. Males that delayed reproduction ultimately reproduced at a larger body size than males that spawned at age 3. Due to size-dependent reproduction within a spawning season, and indeterminate growth, males that delayed re- production also reproduced relatively early within a spawning season. The progeny of males that spawn at age 3 should consequently experience a relatively short period of growth prior to winter; males that delay reproduction should produce progeny that are large at age 1, whereas the progeny of males that spawn at age 3 should be relatively small. These patterns suggest that the association between timing of reproduction and body size within a spawning season will produce a negative paternal effect for age at reproduction such that the life history alternates in successive generations; males that spawn at age 3 produce progeny that delay reproduction and vice versa. Environmental changes at various stages of the life cycle could alter the proportion of males that adopt each tactic. Our findings suggest that details of early ontogeny and inheritance, in combination with estimates of fitness, may be necessary to understand the evolution of life history pathways in some systems.

SEXUAL SELECTION AND FITNESS VARIATION IN A POPULATION OF SMALLMOUTH BASS, MICROPTERUS DOLOMIEUI (PISCES: CENTRARCHIDAE)

Monogamy is often presumed to constrain mating variance and restrict the action of sexual selection. We examined the reproductive patterns of a monogamous population of smallmouth bass (Micropterus dolomieui), and attempted to identify sources of within‐season fitness variation among females and known‐age males. Many males did not acquire a nest site, and many territorial males were unsuccessful in acquiring a mate. The likelihood that territorial males mated depended on several aspects of nest sites. Mated males of age three were larger than the average size of age‐three males in the population. The mean sizes of age‐four and age‐five mated males were not different from the average of same‐age males in the population. Thus, selection resulting from the acquisition of a mate favored large size among only age‐three males. Timing of nest construction and breeding among territorial males was negatively related to male size and did not depend on male age after taking male size into account. Indirect evidence (numbers of eggs deposited in nests) suggests that the timing of spawning among females was also negatively related to female size. Fertility selection favored early reproduction within the season by males of all ages, but large male size was favored among only age‐four males. The combined early breeding of fecund females and female mate choice of large males may explain the positive correlation between the size of age‐four males and the number of eggs acquired. Despite large differences of female fecundity, however, the variance of relative mate number contributed about two times more than the variance of relative fertility among females to the total variance of relative fitness within each sex.

Male and Female Parental Roles in the Monogamous Cichlid, Tilapia mariae, Introduced in Florida

We documented male and female parental roles of a monogamous fish, the spotted tilapia, Tilapia mariae, in channelized rivers in southern Florida, where this species dominated the fish fauna within 10 years of their introduction. Clearly differentiated parental roles existed between males and females, with females performing nearly all tending of embryos and most tending of free embryos. After young became free-swimming and left the nest, however, males took over primary tending of the school of young while the female patrolled the perimeter of the school and performed nearly all chases directed at predators. Male and female T. mariae also traded off vigilance and feeding, and showed a high degree of intrapair coordination. Experimental removal of one or both parents had major effects on parental behavior and brood survival and integrity. Solitary females took on a parental role intermediate between that of the male and female of a pair. Untended broods were attacked by predators and scattered into aquatic vegetation, and were not observed to reform. Under dense nesting conditions we observed adoption of broods, group rearing of free-swimming young and the presence of non-breeder ‘satellites’ sharing and defending a territory with breeders. This highly complex parental care may have allowed T. mariae to invade fish communities dominated by uniparental centrarchids, as well as allowing them to use disturbed habitats such as channelized rivers that are of poor quality for nesting and rearing offspring.

Potentials and pitfalls of integrating data from diverse sources: Lessons from a historical database for Great Lakes stream fishes

opment of databases bringing together scientific information from diverse sources. The enthusiasm has arisen for at least three reasons. First, scientists and resource managers recognize that databases are valuable for making scientifically-defensible decisions regarding fish stocks and their environment. Second, database approaches can increase the integrity and consistency of the data, encourage data sharing among researchers with different areas of expertise, and facilitate the transfer of data among different application programs used for analysis (Harvey and Press 1996). Third, developments in statistics, such as meta-analysis, are improving greatly our ability to summarize what has been done, to examine questions at broader spatial, temporal, and taxonomic scales, and to plan future research (e.g., Osenberg et al. 1999). These developments mean that scientists and resource managers whose primary training may emphasize skills in fisheries management, fish ecology, environmental issues, and policy making, will be asked more frequently to be involved in the construction or management of large databases, or to contribute data or funds to them. On one hand, this is desirable because fisheries scientists are likely to be “closer” to the data and methods of collection, and therefore can improve the quality of the design and analysis of the database (Van Alstyne et al. 1995). On the other hand, this can be problematic if the scientists are unfamiliar with database design and management. Indeed, in some

Biological Effect of Low-head Sea Lamprey Barriers: Designs for Extensive Surveys and the Value of Incorporating Intensive Process-oriented Research

Four sampling designs for quantifying the effect of low-head sea lamprey (Petromyzon marinus) barriers on fish communities were evaluated, and the contribution of process-oriented research to the overall confidence of results obtained was discussed. The designs include: (1) sample barrier streams post-construction; (2) sample barrier and reference streams post-construction; (3) sample barrier streams pre- and post-construction; and (4) sample barrier and reference streams pre- and post-construction. In the statistical literature, the principal basis for comparison of sampling designs is generally the precision achieved by each design. In addition to precision, designs should be compared based on the interpretability of results and on the scale to which the results apply. Using data collected in a broad survey of streams with and without sea lamprey barriers, some of the tradeoffs that occur among precision, scale, and interpretability are illustrated. Although circumstances such as funding and availability of pre-construction data may limit which design can be implemented, a pre/post-construction design including barrier and reference streams provides the most meaningful information for use in barrier management decisions. Where it is not feasible to obtain pre-construction data, a design including reference streams is important to maintain the interpretability of results. Regardless of the design used, processoriented research provides a framework for interpreting results obtained in broad surveys. As such, information from both extensive surveys and intensive process-oriented research provides the best basis for fishery management actions, and gives researchers and managers the most confidence in the conclusions reached regarding the effects of sea lamprey barriers.

NEGATIVE MATERNAL OR PATERNAL EFFECTS ON TACTIC INHERITANCE UNDER A CONDITIONAL STRATEGY

Abstract Alternative behavioral and life‐history tactics are common in animal populations. The conditional strategy model provides a powerful explanation for the evolution and persistence of such tactics, as it allows alternative tactics to be perpetuated even if there is tactic inheritance and tactics yield unequal mean fitness. In many biological systems negative maternal or paternal effects complicate the inheritance of condition and, hence, the inheritance of alternative tactics. Indeed, the inheritance of condition may result in the alternation of tactics across generations. In this paper, we show that the conditional strategy is robust to these effects on progeny condition. There is a unique and stable proportion of tactics under standard inheritance and unequal tactic fitness, and these two important properties of the conditional strategy hold even if negative maternal or paternal effects on progeny condition cause tactics to alternate across generations. However, the dynamics of tactic proportions pursuant to a perturbation of the equilibrium tactic proportions depend on the form of tactic inheritance. An application of our theoretical results to data from a population of smallmouth bass (Micropterus dolomieu) in which negative paternal effects dictate progeny condition reveals that age at first reproduction in males alternates regularly across generations. Furthermore, the model indicates that the population would return rapidly to equilibrium if the proportions of males that mature early or late in life were perturbed from the equilibrium within the system. This example shows how the model of the conditional strategy can be used to gain insight into tactic dynamics in situations where some of the model parameters are difficult or impossible to measure empirically.