The influence of variable rates of inbreeding on fitness, environmental responsiveness, and evolutionary potential.

We manipulated experimental populations of the housefly (Musca domestica L.) under three inbreeding schemes (fast, slow, and punctuated) to partition out the influences of different means and variances in the rate of inbreeding, per generation, while controlling for the final level of inbreeding as a constant. One treatment used constant fast inbreeding (11% per generation; Ne = 4 for 4 generations), for a comparison to one that was consistently slow (3% per generation; Ne = 16 for 14 generations).

QUANTITATIVE GENETIC ESTIMATES OF MORPHOMETRIC VARIATION IN WILD-CAUGHT AND LABORATORY-REARED HOUSEFLIES.

Quantitative genetic estimates of morphometric traits in the housefly, Musca domestica L, were made on parents captured in the wild or reared in the laboratory. Phenotypic variation of morphometric traits declined within the laboratory, but as the additive genetic component of variation also declined, there was no net change in ∗∗∗narrow-sense heritabilities of these traits across environments. Additive genetic variances were inflated only when wild-caught females were used as parents, suggesting that a maternal effect was present.

Effect of Migration or Inbreeding Followed by Selection on Low-Founder-Number Populations: Implications for Captive Breeding Programs.

Using the housefly, Musca domestica (L), as a model system, we tested the ability of two extrems in the range of possible captive breeding protocols to yield sustainable populations following founding with low founder numbers. The protocols tested included two levels of migration as well as inbreeding followed by selection, each with appropriate controls. Each low-founder-number population was founded with two pairs of flies.

AN ANALYSIS OF SELECTIONAL RESPONSE IN RELATION TO A POPULATION BOTTLENECK.

Selection for increased morphometric shape (ratio of wing length to thorax width) was compared between control (nonbottlenecked) populations and bottlenecked populations founded with two male-female pairs of flies. Contrary to neutral expectation, selectional response was not reduced in bottlenecked populations, and the mean realized heritabilities and additive genetic variances were higher for the bottlenecked lines than for the nonbottlenecked lines. Additive genetic variances based on these realized heritabilities were consistent with independent estimates of genetic variances based on parent-offspring covariances.

DIVERGENT AMBULATORY AND GROOMING BEHAVIOR IN SERIALLY BOTTLENECKED LINES OF THE HOUSEFLY.

The extent of genome-wide restructuring predicted in bottleneck models of speciation is addressed in assays of non-reproductive behavior in lines of the housefly. After five serial founder-flush cycles of one of three sizes (1, 4, or 16 pairs), each bottleneck line showed significant differentiation from the outbred control in ambulatory levels and grooming sequences in videotaped records of precopulatory activity. Only one line (4-pair) showed overall lethargy which was associated to inbreeding depression in egg-to-adult viability, thus exemplifying a case of probable extinction due to bottlenecks.

MATING PROPENSITY AND COURTSHIP BEHAVIOR IN SERIALLY BOTTLENECKED LINES OF THE HOUSEFLY.

The efficacy of bottlenecks to stimulate divergence in courtship behavior and consequent premating isolation was tested by serial founder-flush episodes of three sizes (one, four, or 16 pairs) on a population of houseflies established in the laboratory from a single field population. After the fifth founder-flush episode, intraline and interline crosses were performed to detect divergence in mating propensities and patterns of assortative mating. Videotapings of intraline courtships for the bottleneck lines and the control were evaluated for changes in courtship repertoire.

MULTIVARIATE PHENOTYPIC DIFFERENTIATION AMONG BOTTLENECK LINES OF THE HOUSEFLY.

Multivariate phenotypic differentiation in eight morphometric traits was examined in bottleneck lines of the housefly initiated with one, four, or 16 pairs of flies from a natural outbred population. Differentiation was assessed using a Mahalanobis' distance metric in units of additive genetic variance and covariance estimated from the ancestral population (i.e.

EFFECT OF AN EXPERIMENTAL BOTTLENECK ON MORPHOLOGICAL INTEGRATION IN THE HOUSEFLY.

Three measures of multivariate integration were derived from both additive genetic covariance and correlation matrices estimated from parent-offspring covariances to investigate the effect of bottlenecks of different sizes on genetic integration of morphological traits in the housefly, Musca domestica L. Bottleneck lines were initiated with one, four, or 16 pairs of flies sampled from a natural outbred (control) population. Bottlenecks of intermediate size significantly increased the average genetic correlation among traits, resulting in nearly isomorphic variation among all traits in these lines.

A Model of Mating Behavior in Flies.

A model of mating behavior is developed to characterize geographic variation in flies. Normally distributed sexual vigor parameters [Formula: see text] and [Formula: see text] are defined for males and females, respectively. When there is no sexual isolation present, the success and duration of a courtship is determined by the linear difference between the vigors of courting pairs.