Daniel D. Wiegmann

Some Distinguishing Features of Models of Search Behavior and Mate Choice

We develop analytical predictions about how females should behave when either a (infinite time horizon) sequential search tactic or best-of-n rule is employed to search for mates. The likelihood that a male is rejected on first encounter with a female should decline with male quality if females use a sequential search tactic. If females employ a best-of-n rule, however, the probability that a first encountered male is rejected should not depend on male quality; the proportion of males of any quality rejected on first encounter with a female equals the proportion of females that perceive the optimal number of males to be sampled prior to mating to be more than one. The behavior of females using either rule, however, depends on the distribution of quality among potential mates. We show that a variance-preserving increase of mean male quality results in an increase of the critical value of the threshold of acceptance under a sequential search rule; that is, females become more choosy. However, such a shift is not expected to change female search behavior if a best-of-n tactic is employed. A mean-preserving increase of the variance of male quality results in an increase of n among females that employ a best-of-n rule, whereas the number of males sampled prior to mating may increase, decrease, or remain unchanged following such a shift if females use a sequential search rule. The threshold acceptance criterion under sequential search, however, increases (decreases) with a mean-preserving increase (reduction) of the variance of male quality. Patterns of resampling of males by females and the position of accepted males in a search sequence have often been used to distinguish between the best-of-n and sequential search tactics. Predictions of each pattern under a sequential search model depend on both whether the time horizon over which search takes place is assumed to be finite or infinite and whether or not recall (resampling) of previously encountered males is permitted and sometimes resemble predictions of a best-of-n model of search behavior. Because finite time horizon models of sequential search are currently poorly developed, such information is not likely to provide good evidence that females are using either rule The predictions that we derive, however, should be relatively robust to assumptions about recall and the time horizon over which sampling takes place. An experimental protocol in which mate quality is altered may consequently provide a valuable approach to the study of search behavior and mate choice.

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.

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.

Multi-attribute mate choice decisions and uncertainty in the decision process: a generalized sequential search strategy

The behavior of females in search of a mate determines the likelihood that high quality males are encountered and adaptive search strategies rely on the effective use of available information on the quality of prospective mates. The sequential search strategy was formulated, like most models of search behavior, on the assumption that females obtain perfect information on the quality of encountered males. In this paper, we modify the strategy to allow for uncertainty of male quality and we determine how the magnitude of this uncertainty and the ability of females to inspect multiple male attributes to reduce uncertainty influence mate choice decisions. In general, searchers are sensitive to search costs and higher costs lower acceptance criteria under all versions of the model. The choosiness of searchers increases with the variability of the quality of prospective mates under conditions of the original model, but under conditions of uncertainty the choosiness of searchers may increase or decrease with the variability of inspected male attributes. The behavioral response depends on the functional relationship between observed male attributes and the fitness return to searchers and on costs associated with the search process. Higher uncertainty often induces searchers to pay more for information and under conditions of uncertainty the fitness return to searchers is never higher than under conditions of the original model. Further studies of the performance of alternative search strategies under conditions of uncertainty may consequently be necessary to identify search strategies likely to be used under natural conditions.

Individual differences in exploratory and antipredator behaviour in juvenile smallmouth bass (Micropterus dolomieu)

Summary The correlation of individual behaviour in different contexts, known as a behavioural syndrome, constrains the optimization of behaviour within each context. Recent studies reveal that the strength of syndromes differs amongst populations and over individual ontogeny. In this study, exploratory behaviour in an unfamiliar environment and behavioural responses to a simulated predator attack in the presence of food were measured in juvenile smallmouth bass (Micropterus dolomieu). The results revealed a syndrome: individuals who actively explored the unfamiliar environment also behaved more boldly in the presence of the model predator. The syndrome implies a tradeoff between collecting information about one’s environment and risk of a predator attack. Additionally, the results revealed different anti-predator strategies. The simulated predator attack induced a longer period of activity (presumably to disperse away from the predator) by shy individuals, who were also more likely to utilize a refuge, had a longer latency to resume activity and were less likely to resume foraging than bold individuals. Larger conspecifics are the main predators of young-of-year smallmouth bass in the population from which subjects were collected. Predation pressure has been implicated as a cause of behavioral syndromes and the results of this study suggest that cannibalism in high density populations is sufficient to induce behavioural correlations.

Transposition of flower height by bumble bee foragers (Bombus impatiens)

Abstract Honeybees learn visual characteristics of reinforced and non-reinforced flowers in differential conditioning experiments (i.e., experiments that require subjects to choose between a reinforced and non-reinforced flower). In this study bumble bee foragers (Bombus impatiens) were trained in a transposition paradigm to determine if the relational properties of flowers also influence choice behavior. Subjects in one group (group A) were trained with repeated choices between a medium-height flower replete with sucrose solution and an empty tall flower until the medium-height flower was sampled preferentially in five consecutive trials. A second group (group B) was trained on the medium height flower alone for five trials. In a single test trial subjects were given a choice between the medium-height flower and a short flower, each filled with water. A control group showed no preference in this test. Group B subjects showed a significant preference for the medium-height flower and group A subjects that exhibited flower constancy (i.e., sampled only the medium-height flower in training trials) showed an identical pattern of choice. Subjects in group A that sampled both flowers during training, in contrast, transposed flower height and preferred the short flower. These results suggest that the choice behavior of bumble bee foragers is influenced by relational and absolute properties of flowers. The flower characteristics learned by foragers appear to depend on the difficulty of the discrimination problem and the context in which flowers are sampled. Patches of flowers limited in phenotypic variability may produce simple associative learning and flower constancy by foragers.

Effects of a reward downshift on the consummatory behavior and flower choices of bumblebee foragers

Insect foragers often exhibit flower constancy, the tendency to visit single flower types rather than sample alternative flowers that provide equal or higher levels of reward. We employed a negative incentive contrast procedure to examine whether a decrease of sucrose concentration in a regularly visited flower type affects bumblebee (Bombus impatiens) consummatory or choice behavior. Subjects were trained to enter a test arena where they foraged on a single, red, artificial flower that contained 140 microl of sucrose solution. Subjects were reinforced with a concentration of either 0.50 or 0.20 sucrose solution in 20 trials and in 12 subsequent test trials subjects were given a choice between a red and yellow flower that each contained 140 microl of 0.20 sucrose solution. Subjects that experienced a downshift of reward showed an abrupt disruption in consumption of sucrose solution from the red flower. These subjects were also significantly more likely to visit the novel yellow flower than subjects that were reinforced with 0.20 sucrose solution in red flowers in all trials. However, the effects of the downshift of reward were transient and appeared to disrupt consummatory behavior more strongly than flower preferences. These results support the idea that bumblebee foragers form expectations of reward in flowers--as is implied by the results of studies of honeybees--and suggest that unrealized expectations of reward may cause foragers to sample alternative flowers or to fly considerable distances in search of particular types of flowers.

Mate choice and optimal search behavior: Fitness returns under the fixed sample and sequential search strategies

The behavior of a female in search of a mate determines the likelihood that she encounters a high-quality male in the search process. The fixed sample (best-of-n) search strategy and the sequential search (fixed threshold) strategy are two prominent models of search behavior. The sequential search strategy dominates the former strategy--yields an equal or higher expected net fitness return to searchers--when search costs are nontrivial and the distribution of quality among prospective mates is uniform or truncated normal. In this paper our objective is to determine whether there are any search costs or distributions of male quality for which the sequential search strategy is inferior to the fixed sample search strategy. The two search strategies are derived under general conditions in which females evaluate encountered males by inspection of an indicator character that has some functional relationship to male quality. The solutions are identical to the original models when the inspected male attribute is itself male quality. The sequential search strategy is shown to dominate the fixed sample search strategy for all search costs and distributions of male quality. Low search costs have been implicated to explain empirical observations that are consistent with the use of a fixed sample search strategy, but under conditions in which the original models were derived there is no search cost or distribution of male quality that favors the fixed sample search strategy. Plausible alternative explanations for the apparent use of this search strategy are discussed.