Hybridization between escaped domestic and wild American mink (Neovison vison)

The release of domesticated organisms into natural populations may adversely affect these populations through predation, resource competition, and the introduction of disease. Additionally, the potential for hybridization between wild and domestic conspecifics is of great concern because it can alter the evolutionary integrity of the affected populations. Wild American mink ( Neovison vison ) populations may be threatened not only by competition for resources with domestic mink originating from farms, but by breeding with such escapees. Using 10 microsatellite loci, we genotyped mink from Ontario, Canada, sampled from two farms, two putatively mixed populations in regions surrounding the mink farms, and two wild populations with no recent history of mink farming. Using individual-based Bayesian population assignment, we identified four population clusters, including one wild, and three domestic populations. The latter were not clustered by farm but rather by distinct line-bred colour phases. Population clustering also identified domestic and hybrid mink in the free-ranging populations. Nearly two-thirds of the mink sampled in the two putatively mixed populations (78% and 43%) were either farm escapees or descendants of escapees. Principal components analysis of allele frequencies supported our Bayesian assignment results. The power of our assignment test was assessed using simulated hybrid genotypes which suggested that our overall correct classification rate was 96.2%. The overwhelming presence of domestic animals and their hybridization with mink in natural populations is of great concern for the future sustainability of wild mink populations.     

An association between two species of pine aphid, Schizolachnus pineti and Eulachnus agilis

Abstract. 1. Two aphid species feed exclusively on pine needles, Schizolachnus pineti (Fabr.) occupying only the outer (curved) surface with Eulachnus agilis (Kalt.) showing a preference for the inner (flat) surface.
2. Despite E.agilis favouring and S.pineti avoiding senescing needles, both species show a significant tendency to share shoots and needles in the field.
3. The same association is also apparent under laboratory conditions, although E.agilis is randomly distributed between needles in the absence of S.pineti.
4. E.agilis was found to benefit through increased survival and faster growth rates, by feeding on the same shoots and needles as S.pineti.
5. It is suggested that E.agilis may be able to detect and exploit an improvement in the nutritive quality of needles brought about by the feeding activity of S.pineti colonies.     

The usefulness of destructive host feeding parasitoids in classical biological control: theory and observation conflict

Abstract.

• 1 We examine the conventional wisdom among biological control practitioners that destructive host feeding is a desirable attribute in parasitoids employed for classical biological control, using both the predictions of population dynamics theory and historical data on biological control introductions of Hymenoptera against Homoptera.
• 2 Population dynamics theory predicts that destructive host feeders, compared with other parasitoids, are (a) either just as likely or more likely to become established, and (b) unable to depress host equilibria as strongly.
• 3 Analyses of the B IOC AT database suggest that among parasitoids of Homoptera destructive host feeders are superior to other parasitoids with respect to both establishment rate and success rate.
• 4 We present likely explanations for the disparity between the predictions of population dynamics theory and the results of database analysis. A partial explanation for the mismatch between theory and observation with respect to the degree of pest suppression may be that females of destructive host feeding parasitoids rely less upon hosts as a food source when alternative foods such as honeydew and nectar are plentiful.
• 5 We conclude that, despite the predictions of population dynamics theory, destructive host feeders are probably better biological control agents than other parasitoids, and certainly no worse, but that it would imprudent to use destructive host feeding as the sole, or even primary, selection criterion when seeking agents for classical biological control.

     

Replicon Size, Mean Rate of DNA Replication and the Duration of the Cell Cycle and its Component Phases in Eight Monocotyledonous Species of Contrasting DNA C Values

Various aspects of the cell cycle were measured in the apicalmeristem of primary and seminal roots of eight monocotyledonousangiosperms: Oryza sativa (0.6 pg), Zea mays (2.4 pg), Pennisetumamericanum (2.5 pg), Aegilops umbellulata (5.1 pg), Hordeumvulgare (5.5 pg), Triticum monococcum (6.2 pg), Secale cereale(8.6 pg) and Tulipa kaufmanniana (22.6 pg), representing a 38-foldvariation in DNA C values. Using 4-d-old roots of the firstseven species and 21-d-old Tulipa roots, replicon size and ratesof replication were determined by DNA fibre autoradiography,and the duration of the cell cycle and its component phasesby the percentage labelled mitoses method. When tested withDNA C value, no significant relationships existed for repliconsize, rate of DNA replication or duration of G 1. Significantpositive linear relationships were found between DNA C valueand cell cycle duration, duration of mitosis and G2 durationwhen all data were tested, but not when the Tulipa data wereexcluded. The only characters significantly related to DNA C value whenthe Tulipa data were included or excluded were the durationof S-phase, and the ratio of the interval required for a repliconto replicate its allotted DNA (Rs) to the duration of S-phase(Ds). The Rs: Ds ratio is a measure of synchrony of repliconactivation, and the higher the DNA C value the lower this ratiobecame. We concluded that there was a nucleotypic effect ofDNA C value on this ratio and that the interval between activationof replicons became protracted and hence S-phase lengthenedas C value increased. Cell cycle, NA C value, DNA replication, replicon, S-phase