R. F. Rockwell

Life history studies of the lesser snow goose (Anser caerulescens caerulescens). III: The selective value of plumage polymorphism: net fecundity

Between 1969 and 1977 the frequency of the blue phenotype of the dimorphic Lesser Snow Goose (Anser caerulescens caerulescens) showed a steady increase at the La Pérouse Bay colony near Churchill, Manitoba. Cooch (1961, 1963) suggested the global increase resulted from selection pressures favoring blue individuals. The selection hypothesis was evaluated by examining phenotypic differences in net fecundity. We partitioned the reproductive cycle into a series of stages, each defined by a particular index of fecundity. Despite large samples we were unable to detect any significant differences between the two maternal phenotypes in those indices that could conceivably influence population dynamics. We cannot, however, dismiss selection as the mechanism of population change, nor as a contributor to the maintenance of the polymorphism without assessing potential phenotypic differences in viability, age of maturation, and breeding propensity. These attributes are examined in the following paper (Rockwell et al., 1985).

Reproductive performance in lesser snow geese: are two parents essential?

SummaryThe roles of male and female lesser snow geese (Anser caerulescens) in offspring care are well documented, but we know little about flexibility in these roles and how essential they are for offspring survival. We asked whether uni-parental care was adequate, which sex was required at various stages of the reproductive cycle, and what the costs and consequences were of variable amounts of parental care. We found that two parents were important in acquiring nest sites and producing clutches. Widows losing mates during the latter part of laying or in early incubation experienced similar rates of success in hatching clutches to paired females, but males losing mates during incubation experienced total nest failure. Partial clutch loss, hatch loss, intraspecific nest parasitism, duration of incubation periods and gosling weights at hatch did not differ for pairs or widows. In 1983 at La Pérouse Bay, Manitoba, Canada, widows and pairs had similar incubation behaviour, but widows were harassed more and spent more time in full alert posture while on their nests. In 1952 and 1953 at Southhampton Island, Northwest Territories, widows were significantly lighter in body weight prior to hatch than paired females. Thus while widows can bring clutches to hatch successfully, the loss of mates may result in additional physiological costs. Although all possibilities have not been tested experimentally, it appears that costs to uni-parental care up to hatch are not significant. Data collected so far on consequences of uni-parental care provided during the post-hatch period are equivocal, as in one year survival of goslings from single parent broods seemed poor and in another it did not appeart to differ from pairs. The minimum amount of parental care required to raise snow goslings from hatch to recruitment has yet to be determined.

Life history studies of the Lesser Snow Goose (Anser caerulescens caerulescens)

SummaryWe examined the spatial distribution of nesting cohorts of female Lesser Snow Geese (Anser caerulescens caerulescens) in a small colony located at La Perouse Bay, Manitoba. In general, cohorts show a heterogeneous spatial distribution, which arises from a tendency of females of the same cohort affiliation to cluster together. Further-more these associations are maintained through time, such that cohorts tend to dominate particular regions of the colony over several breeding seasons. These findings provide further evidence for breeding site fidelity among female lesser snow geese.

Assortative mating and gene flow in the Lesser Snow Goose: A modelling approach

Abstract Nonrandom mating with respect to color is well documented in the dimorphic Lesser Snow Goose. A set of mathematical models and data from the long-term study at La Perouse Bay, Manitoba, Canada are used to examine various hypotheses advanced to explain the mechanisms behind the assortative mating. Among the factors considered are mate choice based on familial color, accidental formation of genetically unrelated families, and nonuniform distribution of colors in the region where mate selection occurs.

Photobehavioral differentiation in natural populations ofDrosophila: Changes of photoresponse over time inDrosophila pseudoobscura andDrosophila persimilis

The photobehavior of a sympatric assemblage ofDrosophila pseudoobscura andD. persimilis from California was examined over a 13-month period. During that time, certain aspects of the behavior remained constant (e.g., the mean resting photoresponse), while other aspects changed (e.g., the level of genotypic variation of the resting photoresponse ofD. persimilis). The data support the contention of Rockwellet al. [Rockwell, R. F., Cooke, F., and Harmsen, R. (1975).Behav. Genet.5:189–202] that genotypic variation and phenotypic plasticity are central features of photobehavior in natural populations of these species. The evolutionary importance of such genotypic variation and phenotypic plasticity is discussed.

Chromosomal and Behavioral Studies of Mexican Drosophila. V. Frequencies of Multiple Insemination in Three Natural Populations

The detection and measurement of multiple insemination i natural populations contributes directly to our understanding ofmating systems and population structure. Multiply inseminated females in natural populations of Drosophila pseudoobscura have been found in a number of investigations, including those that have studied third-chromosome polymorphisms (Anderson 1974; Levine et al. 1980). The presence of sperm from two or more males in the reproductive tract of a female permits competition between the sperm, allowing selective fertilization to contribute to a males fitness. Selection experiments for reduced time between successive matings in D. melanogaster have been successfully conducted by Pyle and Gromko (1981), indicating the involvement of genetic f.actors in remating tendencies. As with any other genetically influenced trait, it is of interest o investigate whether the tendency of females in natural populations to mate with more than one male varies over space or time. At the spatial level, interpopulation differences in this tendency may reflect adaptations to different ecologies. Over time, such differences might represent behavioral reactions to some changing environmental variable. However, a constancy of remating frequency, especially if found in both spatial and temporal studies, would strongly suggest he existence of longterm evolutionary pressure toward some optimum level of multiple insemination, as it relates to the reproductive physiology of Drosophila. For these purposes, accurate estimates of the level of multiple insemination are desirable.

A Temporal Study of Desiccation Resistance of Sibling Drosophila Species from Laguna Verde, Veracruz, Mexico

-The sibling species, Drosophila melanogaster and D. simulans, were collected periodically from Laguna Verde, Veracruz, Mexico, for 3 yr and tested for desiccation resistance. The number of survivors was recorded after the flies had been kept for 4 h, 8 h and 12 h, at 0% RH, and 20 C. Significant temporal changes in relative survival were found as follows: after the 4 h exposure period for D. simulans and after both 8 h and 12 h for D. melanogaster, females from the first three collections were more resistant to desiccation than males but not from the last two. Comparisons of the species by sex, showed that, except for the 4 h exposure period, D. melanogaster was significantly more resistant to desiccation than D. simulans. There was no indication of seasonal variation in desiccation resistance of males or females of either species at any of the three experimental time periods. However, in the collection of July 1987, some of the flies showed significantly less resistance to desiccation than those of the same sex and species from other collections, as follows: at 4 h, D. simulans males; at 8 h, D. simulans males and females, and D. melanogaster males; at 12 h, D. simulans females and D. melanogaster males and females. These findings are discussed with relation to changes in the relative frequencies of the two species, climatological conditions of the area, and the start-up testing period of a nearby nuclear power plant.

Chromosomal and behavioral studies of MexicanDrosophila. I. Vagility characteristics of three populations ofD. pseudoobscura

Twelve isofemale lines from each of three MexicanDrosophila pseudoobscura populations, known to differ in their degrees of inversion polymorphism, were tested for vagility in the Sakai system. It was found that the flies from the most chromosomally polymorphic population (Zirahuen) had both a significantly lower vagility score and a higher level of expressed genotypic variation for vagility than the flies from the lesser chromosomally polymorphic populations (Amecameca and Tulancingo). The latter two populations could not be distinguished for either parameter of this behavioral trait. The possible role of inversion polymorphism, especially as related to the number of heterozygote combinations formed, in affecting vagility is discussed.

Components of maze running inDrosophila pseudoobscura andDrosophila persimilis

Wild-type and mutant strains ofDrosophila pseudoobscura andD. persimilis were studied for the following maze running activities: frequency of maze completion, rate of progress through the maze, and geotaxis. It was found that these three components of maze behavior were affected to some extent by sex, strain, and species. The significance of these findings in assessing genotype-environment interactions inDrosophila maze studies is discussed.

Chromosomal and Behavioral Studies of Mexican Drosophila. VI. Effects of Density on Larval Digging and Pupation in Drosophila pseudoobscura

Ten isofemale lines of Drosophila pseudoobscura from each of three collecting sites in Mexico were tested at three different densities for porportion of larvae pupating, pupation height, and digging depth. There were no significant differences among the populations for any of the characteristics tested. There were highly significant effects of density on proportion of larvae pupating and pupation height but not on digging depth. These results are discussed with reference to differences in the level of third chromosome inversion polymorphism of these populations and the previously tested vagility behavior.