Search

Habitat loyalty is the tendency of animals to rank a habitat higher, on a scale of preferences which includes several types of habitats, if the parents of the animal came from that habitat. The loyalty matrix is a table of experimentally determined habitat preferences of offspring whose parents originated in different habitats. The trace of the loyalty matrix is a measure of habitat loyalty which is also applicable in the case of single-generation habitat preferences, e.g., the homing behavior of anadromous fish. Procedures for setting confidence limits on the trace are described. A tetrachoric correlation technique applied to the transformed loyalty matrix allows calculation of within-population genetic variance in habitat preference. The correlation between generations is conventionally expressed as heritability. The equilibrium probability vector of the loyalty matrix represents the expected distribution of offspring over substrates; it provides a basis for estimating the magnitude and direction of the...

The iron sulfide that darkens the color of some anaerobic sediment has been tentatively identified as mackinawite (tetragonal FeS) in sediment from Linsley Pond, Conn. The mineral was identified by suspending sediment in solutions saturated with H 2 S at one atm pressure and determining the equilibrium ion activity product (equilibrium IAP) of the reaction: FeS=Fe (super ++) + S (super --) . The IAP was 10 (super -17.7) compared to published values of 10 (super -17.6) for synthetic mackinawite. These values can be assumed to approximate the "solubility product9 of FeS in environments such as the hypolimnia of Linsley Pond and Lake Mendota. Since griegite has been shown to be stable relative to mackinawite in marine sediment, this mineral may be useful in differentiating Fe (super ++) -rich and H 2 S-rich environments in the fossil record.

Gene and genotype frequencies in a polymorphic esterase isoenzyme system were measured in collections of the brittle-star Ophiomusium lymani taken at approximately 2000 meters off the coast of North Carolina. Frequencies varied with the depth of the collections but not with their geographical location along the contours. An excess of a homozygote above Hardy-Weinberg expectation was observed in the deeper samples.

Experiments in iron-rich interstitial water taken from sediment of Linsley Pond, Connecticut have shown that a potential-determining reaction exists for platinum electrodes which do not carry a deposit of ferric oxide (as is generally required in experiments of this type). The stable redox potentials were more negative than predicted by the equation Eh=0.965-0.177pH-0.059 log a Fe ++ by about 100 mv. The oxide layer on the electrode, where present, disappeared slowly in this water as its potential drifted down from an initial value close to the ferrous ion-ferric oxide Nernst potential. Current-potential curves revealed several electroactive substances, none of which could be positively identified with Fe (super ++) ion.

The light-dark preference of individual Spirorbis borealis larvae was measured by the relative amount of time spent in the lighted half of a container. Specimens taken from a tidal pool were 20% more photonegative than those obtained outside the pool, probably because of natural selection against being washed out of the pool at high tide. The between-population behavioural difference was maintained in the laboratory, and is genetic in origin. Applying biometrical genetic analysis to larvae grouped into half-sib families, the within-population variation was used to estimate an upper limit to the heritability of 0.36. It is concluded that the differences among populations greatly exceed heritable variation within populations. A numerical selection model based on the estimated maximum heritability suggests, however, that the populations could diverge by 20% in less than a year, in response to local differences in the selection regime.

The intensity of selection on a trait is measured by (or defined by) the effect that the trait has on fitness. Major components of fitness, such as fecundity, will always be selected in a positive direction (Falconer 1960) when the traits are considered in isolation, with other traits held constant. It is obvious, however, that other traits will rarely be constant in populations of real animals. Most traits, especially such composite life history variables as survival and fecundity, are likely to affect fitness in a number of different ways, simply because they do not vary independently in their phenotypic expression. For example, low- and high-fecundity phenotypes may mature at different ages or show differential survival. Correlation of traits at the level of the phenotype is the net result of genetic correlation (pleiotropism, linkage) and environmental variation that influences two or more traits simultaneously (Falconer 1960).

The group resolved to interpret its terms of reference by considering the following question: “How well can contemporary fisheries science detect, measure, interpret, and predict significant changes in the dynamics of single-species populations in the context of the broader span of marine ecosystems and having regard to both scientific and practical requirements?”

Spirorbis borealis offers a clear-cut example of an important type of variable selection pressure: zygote dispersal, followed by disruptive selection as a pre-adult, followed by mating within subpopulations. It is possible to make quantitative estimates of the intensity of selection on a behavioural polymorphism in this species. Theoretical conditions for protecting polymorphisms against fixation by natural selection have been proposed by Christiansen (1974), Strobeck (1974) and others. The question considered here is whether migration between subpopulations is sufficient to counterbalance the strong selection against one of the phenotypes, using any of the simple, conventional models of inheritance. The work has been done on a Spirorbis population in Terence Bay, approximately 20 km south of Halifax, Nova Scotia.