Doug Cook

A nuclear DNA basis for shelf‐ and bank‐scale population structure in northwest Atlantic cod (Gadus morhua): Labrador to Georges Bank

Variation at five microsatellite DNA loci scored in ≈ 1300 individuals provided evidence of genetic structure among 14 cod (Gadus morhua) populations spanning the range of the species in the northwest (NW) Atlantic. Using DA and DSW measures of genetic distance, as well as FST and RST measures of population structure, differences are revealed among populations at continental shelf scales (NE Newfoundland Shelf, Grand Banks, Flemish Cap, Scotian Shelf, Georges Bank) where regions are separated by submarine saddles, channels and trenches. However, we also provide evidence of genetic structure at spawning‐bank scales consistent with variation in oceanographic features and in the spatiotemporal distribution of spawning, each of which may represent barriers to gene flow among geographically contiguous populations inhabiting a highly advective environment. The differences described are consistent with postdispersal spawning fidelity to natal areas, a behaviour that may be facilitated by topographically induced gyre‐like circulations that can act as retention mechanisms. Significant degrees of substructure among neighbouring and contiguous cod populations may be most easily explained by the associated oceanographic features and processes that conceivably form the template for the evolution of the structure. We suggest that bathymetric and hydrodynamic structure represents a rational starting point for developing hypotheses to examine the processes that lead to the genetic structuring of marine fish species.

Stability in the historical pattern of genetic structure of Newfoundland cod (Gadus morhua) despite the catastrophic decline in population size from 1964 to 1994

We report on evidence of long term stability inthe geographic pattern of geneticdifferentiation among cod (Gadus morhua)collected from 5 spawning banks offNewfoundland and Labrador over a periodspanning three decades (1964–1994) and 2orders of magnitude of population sizevariation. Six microsatellite DNA lociamplified from archived otoliths (1964 and1978) and contemporary (1990s) tissue samplesrevealed fidelity to natal spawning banks overthis period. A two level (spawning bank anddecade) hierarchical and multilocus AMOVAindicated that 1.55% of the total variation inallele frequencies could be attributed(P = 0.036) to spatial structure while novariance component could be attributed totemporal changes. A finer scale analysis amongcod from just 3 of these spawning banksreveals, however, evidence consistent with somepost-collapse mixing between cod from twobanks. In the context of fisheries managementand conservation, the survival of the spatialpattern of genetic differentiation during thepopulation collapse suggests that if recoveryeventually occurs it will likely be throughpopulation re-growth in situ rather thanby migratory influx.

A review of the evidence for genetic structure of cod (Gadus morhua) populations in the NW Atlantic and population affinities of larval cod off Newfoundland and the Gulf of St. Lawrence

Abstract We review our recent studies on the genetic structure of Atlantic cod (Gadus morhua) populations in the NW Atlantic. Our conclusions are based on knowledge of polymorphism at microsatellite DNA loci combined with known aspects of cod biology and ecology and with known oceanographic features in the NW Atlantic. Three case studies illustrate genetic heterogeneity between cod populations at the meso- and large-scales of coastal embayments and offshore banks and at the small-scale of oceanographic features. Our results generally highlight the importance of combining genetic with physiological, ecological, and oceanographic information, when assessing the genetic structure of highly abundant, widely distributed, and high gene-flow marine fish species. We highlight the role that oceanographic features (e.g., gyre-like systems) and known spatio-temporal differences in spawning time may play as barriers to gene-flow between and among neighboring and often contiguous cod populations in the NW Atlantic. We suggest that bathymetric and hydrodynamic/oceanographic structure represents a rational starting point for developing hypotheses aimed at assessing the genetic structure of high gene-flow marine fish species.

Isolation of salmonid microsatellite loci and their application to the population genetics of Canadian east coast stocks of Atlantic salmon

Abstract Genetic variation at four microsatellite loci, two isolated from Atlantic salmon and two from rainbow trout, was assayed in five populations of Alantic salmon from Nova Scotia, Canada and in samples from Norway and Ireland. Up to 38 allelles per locus and heterozygosities of 0.9 were observed at some loci. Genetic distances, calculated over the four loci for all population samples show a clear grouping of populations according to geographic location. These loci show potential as genetic markers in Atlantic salmon due to the range of polymorphisms observed among individual loci and to the ease and speed of sample assay. Highly variable loci will be of use in the ‘genetic tagging’ of cultured fish and in the assessment of levels of gene introgression from cultured to wild stocks. The clear differences in both allele frequencies and alleles observed between continents will be of value in the assessment of the relative sizes of the contributions of Canadian and North European salmon to the mixed fishery off Greenland.

Parasitism-induced hemolymph polypeptides in Manduca sexta (L.) larvae parasitized by the braconid wasp Cotesia congregata (Say)

Parasitization of newly ecdysed third, fourth, or fifth instar Manduca sexta larvae by the gregarious braconid wasp Cotesia congregata induces synthesis of new hemolymph proteins in the host. Analysis of hemolymph from parasitized and unparasitized control larvae using SDS gel electrophoresis showed that a major 33 kd band, plus several minor bands, were synthesized in parasitized but not control larvae; autoradiograms of proteins labeled in vivo for 1 hr with [35S]methionine indicated that synthesis of the 33 kd polypeptide began a few hours following oviposition by the wasp. Synthesis of the 33 kd parasitism-specific polypeptide was induced in unparasitized larvae by the injection of ovarian calyx fluid from adult female wasps; this fluid is known to contain two morphologically distinct types of virus particles that are normally injected into the host along with eggs during parasitization. Exposure of calyx fluid to psoralen in the presence of long-wave u.v. light destroyed its capacity to induce synthesis of the 33 kd protein, suggesting that synthesis of this polypeptide may be mediated by viral nucleic acid.

MIXED‐STOCK ANALYSIS OF ATLANTIC COD NEAR THE GULF OF ST. LAWRENCE BASED ON MICROSATELLITE DNA

The collapse of various stock complexes of cod (Gadus morhua) in the northwest Atlantic has prompted a clarification of relationships among stock components. Here we examine the genetic composition of >2300 cod collected during 1994-1997 in the Gulf of St. Lawrence and its approaches to determine whether: (1) stock components can be genetically identified; (2) population structure is temporally stable; (3) components are always separated and, if not, where and when are they mixed; and (4) component contributions to mixtures can be estimated. We use polymorphism at six microsatellite DNA loci from cod collected on or near their spring and summer spawning grounds to examine structure and then employ maximum likelihood analyses to estimate contributions of each component to mixtures overwintering near the entrance to the Gulf. Estimates of genetic structure (FST and RST) reveal significant differences among cod populations during stock- separated periods, and the structure appears to be temporally stable. Multidimensional scaling analysis of estimates of genetic distance (DA) suggest that the structure results from differences among cod collected within the Gulf of St. Lawrence and those collected near the entrance to the Gulf on either side of the Laurentian Channel in the Cabot Strait, as well as among cod collected south of Newfoundland along the north side of the Channel. Weak genetic heterogeneity among seven regional mixed-stock collections during the over- wintering period suggests that cod aggregations characteristically found in the overwintering region represent population mixtures that differ in the proportion of cod contributed to them by the various stock components. Maximum likelihood estimates indicate no signif- icant temporal changes in component contributions to the mixed-stock samples between 1996 and 1997. when all of the winter mixed-stock samples were pooled. The combined contribution of cod from the southern and northern Gulf of St. Lawrence to the. mixed- stock samples ranged between 46% and 71% (expected 64%). More precise estimates of contributions from these two regions are precluded by the weak genetic differentiation detected in our samples. The contribution by cod from the Cape Breton Island region was small and estimated at 3%. Contributions by cod from the eastern Scotian Shelf, southwest Newfoundland and south-central Newfoundland were in the range of 13-14%, 4%, and 8%, respectively. Contributions by inshore cod from Placentia and Fortune Bays in south Newfoundland were small to negligible (-3% each). The results indicate that future man- agement could be designed around the spatial and temporal scale of the stock structure identified during the stock-separated period and around the spatially varying contributions to the overwintering mixed-stock fishery.

Induction of a new haemolymph glycoprotein in larvae of permissive hosts parasitized by Campoletis sonorensis

Abstract Parasitization by Campoletis sonorensis consistently results in the appearance of a new polypeptide, a glycoprotein, in several habitual host species. This occurs prior to the hatching of parasitoid eggs, and can be duplicated by the injection of either calyx fluid or purified C. sonorensis virus. Oviposition in two non-permissive hosts. Anticarsia gemmatalis and Mamestra configurata, leaves haemolymph polypeptide profiles unchanged.

An Unusual Virus from the Parasitic Wasp Cotesia melanoscela

Certain strains of the braconid parasitoid Cotesia melanoscela carry two different viruses within their ovaries, one of which (here designated CmV2) is apparently not a polydnavirus. Virus replication occurs in the ovarian calyx and in some other tissues of both male and female parasitoids; as yet, no replication has been observed in the testis, however. In addition, CmV2 is one of only two parasitoid viruses known to replicate in host insect larvae, and we not show that this virus is also capable of replicating in vitro; the virus is nevertheless nonpathogenic for gypsy moth larvae. The virus is not transmissible per os, either to host animals or to larvae of parasitoid strains lacking it. CmV2 is stably maintained within strains carrying it apparently by a vertical transmission mode involving the maternal line; transmission via the male germ line could not be demonstrated. While purification of the virus was not achieved, preliminary work allows us to suggest the genome consists of a single double-stranded DNA molecule of approximately 125 kb.

Comparative serology of viruses isolated from ichneumonid parasitoids.

Serological relationships among viruses isolated from the ovaries of some ichneumonid wasps have been examined by immunoblotting. An antiserum prepared against purified Hyposoter exiguae virus reacted with polypeptides of calyx fluids isolated from species belonging to several different ichneumonid genera. Significant cross-reactions, however, were confined to three genera and usually involved only two to four polypeptides.

Purification and preliminary characterization of insect spherulocytes

Abstract Spherulocytes were purified from the haemolymph of two lepidopteran species, Heliothis virescens and Malacosoma disstria . Analysis by polyacrylamide gel electrophoresis revealed the presence of two to four major polypeptides of relatively low molecular weight in purified M. disstria cells and one or two in H. virescens spherulocytes. A sulphated glycosaminoglycan-like substance was extracted from the purified cells.