David M. Lambert

Genetics of Potamopyrgus antipodarum (Gastropoda: Prosobranchia) : evidence for reproductive modes

Abstract Individuals from six bisexual and six unisexual populations of Potamopyrgus antipodarum were examined electrophoretically, in order to determine their mode of reproduction. Extensive genetic variation within populations was revealed at four of seven presumptive loci, with no differences between unisexual and bisexual populations being observed. In addition, extensive heterogeneity was observed for both reproduction types. Examination of the genotypes of parents and offspring indicated that individuals from bisexual populations reproduced sexually whereas those from unisexual populations demonstrated ameiotic parthenogenesis.

A genetic analysis of populations of Galaxias maculatus from the Bay of Plenty: Implications for natal river return

Abstract An electrophoretic analysis of four diadromous populations of Galaxias maculatus (Jenyns) from rivers within the Bay of Plenty region was conducted to determine evidence for genetic structuring. Permanent genetic divergence might be expected if individuals consistently returned to their natal rivers. A contingency χ2 analysis of five of the eleven presumptive loci revealed significant differences among the four populations for two loci. Two loci also exhibited significant differences from expected frequencies of genotypes for pooled data, indicating possible divergence from random mating. However, the level of genetic differentiation, as measured by Wrights F coefficient, is low (FST = 0.055). We suggest that the degree of differentiation recorded is a likely result of high mortality at the larval stage, but that temporal sampling should conclusively distinguish between temporal differentiation and differentiation resulting from a structured population.

Evolutionary Studies of the New Zealand Coastal Mosquito Opifex Fuscus (Hutton) I. Mating Behaviour

Das Fortpflanzungsverhalten der Stechmucke Opifex fuscus wurde im Laboratorium und in der Natur, an einer felsigen Kuste auf der Nordinsel von Neuseeland, beobachtet. Diese Art hat ein aussergewohnliches Paarungssystem. Im Gegensatz zu den meisten Arten der Steckmucken, die sich im Flug paaren, geschieht die Paarung der Opifex auf der Wasseroberflache der Salzwassertumpel, aus denen die erwachsenen Stechmucken ausschlupfen. Die Mannchen ergreifen und bewachen mannliche und weibliche Puppen die kurz vor dem Ausschlupfen sind, und im Falle einer weiblichen Puppe fangt die Paarung an, kurz bevor das Weibchen vollig ausgeschlupft ist. Das Geschlechtsverhaltnis zur Zeit der Paarung (oder Operational Sex Ratio - siehe EMLEN & ORING (1977) war ungefahr 1 Weibchen auf 260 Mannchen in der Natur. Das Paarungsverhalten wird ausfuhrlich beschrieben, und andere relevante Beobachtungen im Laboratorium und in der Natur werden berichtet. Fruhere Beschreibungen des Paarungsverhaltens und die Hypothesen, die sich mit der evolutionaren Bedeutung dieses Verhaltens befassen, werden im Hinblick auf unsere Beobachtungen besprochen. Eine alternative Hypothese fur die Evolution des Paarungssystems bei den Opifex wird vorgeschlagen. Wir sind der Meinung dass die naturliche Auslese, die durch die Konkurrenz zwischen den Mannchen, um Zugang zu den Weibchen zu erlangen, verursacht wird, wahrscheinlich ein bedeutender Faktor bei der Evolution des Ergreifens und Bewachens von Puppen gewesen ist.Summary The reproductive behaviour of the mosquito Opifex fuscus was observed in the laboratory, using video equipment, and in nature, on a rocky shore in the North Island of New Zealand. This species has an unusual mating system. In contrast with most mosquito species, which mate in flight, mating in Opifex takes place on the water surface of the salt-water pools from which the adults emerge. Males grasp and guard male and female pupae which are close to emergence, and, in the case of a female pupa, copulation begins just before the female has completed emergence. The sex ratio at the time of mating (or Operational Sex Ratio - See ENtLerr & ORING, 1977) was found to be approximately 1 female to 260 males in the field. The mating behaviour is described in detail and other relevant laboratory and field observations are reported. Previous descriptions of the mating behaviour and hypotheses regarding its evolutionary significance are discussed in the light of our observations. An alternative hypothesis is proposed regarding the evolution of the Opifex mating system. We argue that natural selection caused by competition among males for access to females is likely to have been a major factor responsible for the pupal grasping and guarding behaviour.

Genetics of Potamopyrgus antipodarum (Gastropoda: Prosobranchia): Variation in unisexual populations

Abstract The New Zealand gastropod Potamopyrgus antipodarum comprises both unisexual and bisexual populations. The aim of this study was to examine the genetic variation of unisexual populations and to determine whether the variation observed was consistent with the predictions of ameiotic or meiotic parthenogenesis. Genetic variation within and among eight unisexual populations of P. antipodarum (four from the Auckland region and four from the Rotorua region) was examined for seven presumptive loci. The results indicated extreme genetic divergence both within populations, among populations within each region, and between regions. In many instances a significant excess of heterozy gotes was noted, suggesting ameiotic parthenogenesis. The finding of genetic divergence within individual populations is not consistent with the one-clone one-population hypothesis generally postulated for ameiotic parthenogens. Possible origins of this variation are discussed.

A cladistic analysis of species of the molluscan genus Potamopyrgus based on allozyme data

The relationships among four species of the molluscan genus Potamopyrgus have been investigated using cellogel electrophoresis. Electrophoretic variability at nine presumptive loci was calculated. Cladograms were constructed using both electromorph and locus as characters. Results indicate two major groupings within the genus. P. estuarinus and P. pupoides appear to represent sister taxa and, as a grouping, are closely related to P. antipodarum. The relationship of P. troglodytes to other species of the genus remains problematical. The cladograms obtained are congruent with that based on morphology with respecttoP. antipodarum, P. estuarinus, and P. pupoides.

Evolutionary Studies of the New Zealand Coastal Mosquito Opifex Fuscus (Hutton) Ii. Competition for Mates

In the mating aggregations of Opifex fuscus, as in those of many other dipterans, the Operational Sex Ratio is strongly biased towards males. Male Opifex swarm on the water surface of the salt-water pools from which the adults emerge. They grasp pupae and mate with emerging females. We here present evidence for non-random mating among males with respect to body size, and discuss our results in relation to other species with similar mating systems. Our results suggest that reproductive competition among males has been an important factor in the evolution of the apifex mating system.

Cytogenetics of New Zealand blackflies of the genus Austrosimulium (Diptera: Simuliidae) 1. The cytogenetics of Austrosimulium australense

Abstract This study undertakes a cytogenetic analysis of the New Zealand blackfly species Austrosimulium australense (Schiner). The principles of such an approach are outlined, and previous taxonomic studies of the genus Austrosimulium, in particular the taxonomic position of A. australense, are discussed. Populations from North Island localities covering a wide area were sampled and analysed for polymorphisms in the polytene chromosomes, taken from salivary glands of larvae. In all, 1018 larvae from 49 sites were analysed. A polytene chromosome map of A. australense is presented, with details of chromosomal inversions found in salivary gland cells. Three geographical zones are designated, according to the incidence of certain chromosomal polymorphisms.

The ‘good old days’ of evolutionary biology? A review of the SYSTANZ meeting on evolution, Greta Point, Wellington, 3 September 1982

Abstract In 1978 George C. Williams predicted that the last two decades of this century would be a fabulous age, and that evolutionary biology would provide critical insights into the processes of change in the biological world. He suggested that these might come to be described as the “good old days”. I am not so sure that this is likely, but I am very sure that it will be a turbulent time. I think also that those biologists who attended the recent SYSTANZ meeting on evolution must by now be equally convinced. The conference was punctuated by heated debates on major topics such as Darwinian and neo-Darwinian theory, vicariance biogeography, and teleology, to mention but a few.