Laboratory Mating Experiments Research Articles

Mechanical use of crayfish chelae

Chela mechanical function was investigated by comparing individuals of the crayfish Orconectes propinquus (Girard) with and without the mechanical use of their chelae (dactyls held closed with rubberbands or glue) to determine if crayfish need the mechanical function of chelae to feed, to deter predators, to survive in the field, and to copulate with mates. Laboratory studies showed that crayfish did not require the use of their chelae to consume algae or snails, but fewer crayfish consumed juvenile insects when their pincers were non‐functional. Male and female crayfish with functional pincers were just as susceptible to snapping turtle predators in the laboratory and just as likely to be recaptured in the field as those with non‐functional pincers. Laboratory mating experiments with two males and a single female showed that only males with the mechanical use of their chelae copulated. These results indicate that O. propinquus require their chelae for mating but do not require functioning chelae to feed ...

The construction, detection and use of bioluminescent Rhizobium leguminosarum biovar trifolii strains

A. CRESSWELL, L. SKOT AND A.R. COOKSON. 1994. The gene encoding the firefly luciferase enzyme (luc) was introduced to Rhizobium leguminosarum biovar trifolii strains with a view to using the resulting bioluminescent strains to study the survival of genetically-engineered rhizobia in soil microcosms. The genetically-engineered micro-organisms (GEMs) behaved similarly to their parent strains with respect to growth rate in laboratory media and in their symbiotic performance with their host plants. No gene transfer could be detected in laboratory mating experiments. When inoculated onto a non-sterile soil the population of the GEM declined sharply from an initial cell density of 2 times 1077 g-1 soil to approach a stable cell density of approximately 3 times 102 g-1 after 150 d. Direct photography of bioluminescent rhizobia enabled the detection of colonies as small as 0.1 mm in diameter without the need for transferring colonies onto filter paper. When a Rhizobium strain carrying the luc marker on a plasmid was used as inoculant it was possible to visualize differences in colonization of the rhizosphere of white clover and ryegrass by contact print and colour transparency films. The photographic detection methods described here demonstrate the possibilities of using bioluminescent rhizobia for assessing their survival in soil, and for looking at rhizosphere populations which may be an important site for potential gene transfer.

Response of males to female sex pheromone in the orange wheat blossom midge,Sitodiplosis mosellana (G�hin) (Diptera: Cecidomyiidae)

Males of the orange wheat blossom midge,Sitodiplosis mosellana (Géhin), were attracted by female but not by male extract in a Y-tube bioassay. In laboratory mating experiments, females exhibited typical calling behavior under all conditions tested. At 19‡C in the dark, males exhibited a high frequency of wing vibration (a courtship behavior) and mating attempts, and 68% of females were mated. However, there was virtually no courtship or mating activity at 17‡C and 23‡C (0 and 11% mated, respectively); at 21‡C, there was an intermediate level (43% mated). Light intensity of 1500 lux (as compared to darkness), or high relative humidity (96%, as compared to 70%) also inhibited mating activity. In trapping experiments in a wheat field, males but not females were caught in significantly greater numbers in traps baited with a solvent extract of virgin females, as compared with unbaited traps, at a trap height of 20 cm. At a trap height of 60 cm above ground, no males were caught. Males did not differentiate between traps baited with two calling females and a solvent extract of two virgin females, and the latter lost little activity over 48 hr under field conditions. There was a daily rhythm of male response to receptive females or female extract each evening between 1700 and 2200 hr CST. The sensitivity of males to environmental conditions and their consequent short daily period of response in the field are thought to be related to their high susceptibility to desiccation and lack of sources of food as adults.

Mating system, optimal number of matings, and sperm transfer in the Argentine ant Iridomyrmex humilis

In ants, because males have a finite sperm supply and females mate only at the beginning of their reproductive lives, it is possible to infer which is the limiting sex from a few parameters: the amount of sperm produced by males, the amount of sperm stored by females, and the numerical sex ratio. In the Argentine ant Iridomyrmex humilis mating takes place in the nest. Laboratory experiments and field data showed that the numerical sex ratio is heavily male-biased (10.1:1) and that the maximum number of sperm a female can store is similar to the number of sperm a male possesses. Thus females are the limiting sex in this species. In a set of mating experiments, one queen was presented with 1–20 males. The highest proportion of successful matings occurred when females were presented with two males. There was a significant negative correlation between the amount of sperm queens stored and the number of males present in the mating arena. This relationship most likely resulted from male interference during the copulation process. When several males were present in the arena, the mating pair was frequently disturbed by other males trying to copulate. Newly mated queens collected from the field stored 172,000 ± 76,000 sperm, a quantity most similar to that measured in laboratory mating experiments with a ratio of 5 or 10 males per queen. Because the operational sex ratio in I. humilis is highly male-biased, male interference may also decrease the amount of sperm queens store in the field. In many ants, fewer sperm stored by queens should decrease their reproductive success because they would run out of sperm earlier in their reproductive lifetimes. However, comparison of the amount of sperm present in young and old I. humilis queens collected in the field suggests that most use only a small proportion of their sperm supply during their lifetimes. Males mate once and discharge all their sperm during a single mating. Females may mate with several males but dissection of these males indicated that in most cases only one of them had empty seminal vesicles thus suggesting that a single male is responsible for most of the sperm transfer. Thus caution should be exercised in inferring multiple inseminations, as is frequently done in eusocial insects, from the observation of multiple copulations.

Estimating the degree of sperm precedence in laboratory mating experiments: a maximum likelihood method.

Allozyme polymorphisms have been used frequently in laboratory mating experiments to study patterns of sperm utilization in multiply mated females. In some instances, due either to chance or to design, there is a diagnostic difference between male genotypes that allows unambiguous assignment of paternity. In other instances, there is some overlap in allelic composition of males, so that attribution of paternity is often uncertain. This paper presents a statistical method for analyzing data of the second sort obtained from twice-mated females, based on the principle of maximum likelihood. The method allows the estimation of a mating parameter, psi the frequency with which sperm from the first male fertilizes the female's eggs. Various hypotheses about the null value of psi may be tested by a likelihood ratio test statistic. Also presented is a method of testing for homogeneity in psi values across different broods produced by the same female.

Controlled Mating, Karyology, Morphology, and Sex-Ratio in the Dendroctonus ponderosae Complex12

Laboratory mating experiments and observations on developmental rate, karyology, and morphology confirm the recent synonymy of Dendroctonus monticolae Hopkins with D. ponderosae Hopkins, but establish the species integrity of D. jeffreyi Hopkins, also previously considered a synonym of ponderosae. D. monticolae from British Columbia and 8 California localities were interfertile and morphologically similar. D. ponderosae from Colorado were interfertile with monticolae from California, but their mean pronotal widths, 2.44 mm and 2.10 mm, respectively, and indices of pronotal punctation, 5.43 and 6.12, respectively, were very significantly different. D. monticolae and its hybrid with ponderosae showed the karyotypic formula 11AA + Neo-XY. D. jeffreyi is larger (pronotal width = 2.63 mm) and its pronotum less densely punctured (index = 4.19) than monticolae and ponderosae. The karyotype of jeffreyi is also 11AA + Neo-XY, but the Neo-X is usually constricted and 1.4 times longer than the Neo-Y while the Neo-X of monticolae is rarely constricted and only slightly larger than the Neo-Y. In addition, a tiny supernumerary chromosome was present in some jeffreyi. In reciprocal pairings of monticolae and jeffreyi, none of the 846 eggs laid by 21 monticolae females hatched, but 8 larvae and 1 sterile female resulted from 362 eggs laid by 10 jeffreyi females. Five pairings of jeffreyi and pondcrosae produced no brood. Several jeffreyi (control) pairings showed a marked reduction in egg hatchability and only female progeny were produced. A male-lethal factor attacking the embryos is suggested, but pedigree data are insufficient to determine whether chromosomal or cytoplasmic factors are involved.