Response to bidirectional and reverse selection for mating behavior in Japanese quail Coturnix coturnix japonica

Responses to relaxed and reverse selection in strains artificially selected for duration of death-feigning behavior in the red flour beetle, Tribolium castaneum

Divergent lines selected artificially for many generations make it possible to answer two questions: (1) whether genetic variation still exists within the selected population; and (2) whether the selection itself is costly for the selected strain. In previous studies, the red flour beetle Tribolium castaneum was divergently selected artificially for duration of death-feigning, and strains selected for longer (L-strain) and shorter (S-strain) durations of death-feigning have been established (Miyatake et al. 2004, 2008). Because the selection experiments have been conducted for more than 27 generations, genetic variation may be eroded. Furthermore, because another previous study reported physiological costs to L-strains, the L-strains selected artificially for longer duration of death-feigning may have suffered more costs than the S-strains. In the present study, therefore, we relaxed the selection pressure after the 27th or 30th generation of S- and L-strains. We also carried out reverse selection during the most recent eight generations of S- and L-strains. The results showed that each strain clearly responded to relaxation of selection and reverse selection, suggesting that (1) additive genetic variation still existed in both strains after long-term selection, and (2) selection for shorter and longer duration of death-feigning was costly. These results suggest that anti-predator behavior is controlled by many loci, and longer or shorter duration of death-feigning is costly in a laboratory without predators.

Genetic and Genomic Response to Selection for Food Consumption in Drosophila melanogaster

Food consumption is an essential component of animal fitness; however, excessive food intake in humans increases risk for many diseases. The roles of neuroendocrine feedback loops, food sensing modalities, and physiological state in regulating food intake are well understood, but not the genetic basis underlying variation in food consumption. Here, we applied ten generations of artificial selection for high and low food consumption in replicate populations of Drosophila melanogaster. The phenotypic response to selection was highly asymmetric, with significant responses only for increased food consumption and minimal correlated responses in body mass and composition. We assessed the molecular correlates of selection responses by DNA and RNA sequencing of the selection lines. The high and low selection lines had variants with significantly divergent allele frequencies within or near 2081 genes and 3526 differentially expressed genes in one or both sexes. A total of 519 genes were both genetically divergent and differentially expressed between the divergent selection lines. We performed functional analyses of the effects of RNAi suppression of gene expression and induced mutations for 27 of these candidate genes that have human orthologs and the strongest statistical support, and confirmed that 25 (93 %) affected the mean and/or variance of food consumption.

Short-term spatial memory responses in aged Japanese quail selected for divergent adrenocortical stress responsiveness

Stress-induced glucocorticoids can dampen learning and spatial memory via neuronal damage to the hippocampus. Cognition losses can be transient (associated with acute stress episodes) or permanent as in aged individuals who show chronic glucocorticoid-induced accelerated brain aging and neurodegeneration (dementia). Thus, chronic versus acute stress effects on spatial memory responses of quail selected for reduced (low stress, LS) or exaggerated (high stress, HS) plasma corticosterone (B) response to brief restraint were assessed. Aged food-motivated male LS and HS quail were tested for 10 min in a feed-baited 8-arm radial arm maze (RAM) 1) at 255 d of age (quail who had experienced lifelong management stressors but who were otherwise never intentionally stressed; that is, chronically stressed birds), 2) on the next day post-acute stressor treatment (5 min of restraint), and 3) on the next day without treatment (acute stress recovery). The RAM tests used the win-shift procedure in which visited arms were not rebaited. Radial arm maze performance was measured by determination of the total number of arm choices made, the number of correct entries made into baited arms out of the first 8 choices, the time required to make a choice, and the number of pellets eaten. Line effects (P < 0.001 in all cases) were detected for total number of arm choices made (HS < LS), number of correct entries made into baited arms out of the first 8 choices (HS < LS), time required to make a choice (HS > LS), and number of pellets eaten (HS < LS). However, neither the effects of day of RAM testing nor its interaction with line further influenced these variables. Thus, although selection for divergent plasma B responsiveness to an acute stressor was found to be associated with severe impairment of spatial memory in aged male HS compared with LS quail, the observed spatial memory impairments (HS > LS) could not be further altered by acute stressor treatment. Line differences in cognition may reflect lifelong management-induced stress episodes that periodically produce higher plasma B responses in HS than LS quail, which underlie HS quail memory deficits, or other etiologies, or both.

Locomotor activity responses to ethanol, other alcohols, and GABA-A acting compounds in forward- and reverse-selected FAST and SLOW mouse lines

Mice selectively bred for high (FAST) or low (SLOW) locomotor stimulant response to ethanol have been found to differ in response to drugs with gamma-aminobutyric acid (GABA)-ergic actions. Reverse selection produced lines that are similar in sensitivity to ethanol stimulation (r-FAST and r-SLOW) and provided a unique model for testing hypotheses about shared genetic influence on sensitivity to ethanol and GABAergic drugs. FAST mice were more stimulated than SLOW mice by all drugs tested: ethanol, methanol, n-propanol, t-butanol, pentobarbital, diazepam, and allopregnanolone. In contrast, r-FAST and r-SLOW mice differed in sensitivity to only a few isolated drug doses. Locomotor responses of each reverse-selected line were significantly different from the responses of their respective forward-selected line for all drugs. Results support an effect of selection for ethanol sensitivity on allosteric modulation of the GABA-A receptor.

Heterosis following long-term bidirectional selection for mating frequency in male Japanese quail

Reciprocal crosses (sire line shown first and dam line second) among high (H) and low (L) selected lines and the randombred control line (C), which was the base population for the selected lines, were made after 40 generations of bidirectional selection for mating frequency of male Japanese quail. Significant heterosis for the selected trait was found only in crosses between Lines C and L, being 62 and 92% for LC and CL, respectively. Heterosis for percentage of maters was present in all crosses, ranging from 8% for HC and CH to 46% for HL. Three (HC, LH, and CL) of the six crosses had significant heterosis for both 4- and 8-wk BW. Heterosis for 4- and 8-wk BW was also significant for the HL and CH crosses, respectively. For area of the cloacal gland, heterosis was significant in five crosses. Although crosses tended to exhibit higher relative aggressiveness than their respective midparent means, heterosis for this trait was not significant. Reciprocal effects, although not important for most traits, were present for BW in crosses between Lines C and L and Lines H and C. In general, long-term selection for mating frequency of males changed the genetic basis of selected and correlated traits with considerable nonadditive genetic effects observed for most traits in specific crosses.

Adaptation, Exaptation, and Constraint: A Hormonal Perspective

We approach conceptual issues in evolutionary biology from an endocrinological perspective, noting that single hormones typically act on several target tissues and thereby mediate suites of correlated phenotypic traits. When several components of such a suite are beneficial, an important evolutionary question is whether all are adaptations or some are exaptations. The answer may depend on whether the traits arose in response to selection on variation in systemic levels of the hormone on variation in responsiveness of target tissues to invariant levels of the hormone. If the former, selection probably acted directly on fewer than all traits; beneficial traits arising indirectly would be exaptations. In contrast, multiple beneficial traits that arose out of independent changes in target-tissue sensitivity to invariant hormone levels could all be adaptations. Knowledge of specific hormonal mechanisms as well as of historical selective regimes will be necessary to draw such distinctions. Endocrine constraints on evolution can be studied experimentally by applying hormones systemically and measuring interdependent responses of beneficial and detrimental traits to selection (phenotypic engineering with hormones). Supposing that alteration of one trait in isolation would enhance fitness, cases in which the net effect of endocrine alteration of multiple traits is to depress fitness provide evidence for constraints. We briefly report results of recent studies employing hormonal manipulations, stressing our own work on the dark-eyed junco (Junco hyemalis: Emberizidae).

Forty generations of bidirectional selection for mating frequency in male Japanese quail

A bidirectional replicated selection experiment for high (H1 and H2) or low (L1 and L2) cumulative number of complete matings (CNCM) in male Japanese quail was conducted for 40 generations. In the S32 generation, a subline was taken from each selected line and selection was relaxed. In the randombred control line (C), CNCM and unselected traits changed significantly over generations. Means of the selected lines were adjusted each generation for deviations from the control means. After 40 generations of selection, there was a 21-fold difference in CNCM (59.4 vs 2.8) between Lines H1 and L1. Whereas means increased and variation decreased in the high lines, means decreased and variation increased in the low lines. Regressions of mean CNCM on generation of Lines H1, H2, L1, and L2 were 1.15 +/- 0.08, 0.61 +/- 0.08, -0.26 +/- 0.04, and -0.34 +/- 0.03, respectively. Although responses to selection were observed throughout the 40 generations in Line H1, the low lines appeared to have reached a limit to selection after the S30 generation. Relaxed lines provided supporting evidence for this conclusion. Mean CNCM decreased in the relaxed high lines to that of the control, whereas the low relaxed lines remained at the same level as their corresponding selected lines. Line H2 went into extinction in the 37th generation as a result of reduced fitness. Realized heritabilities of CNCM were 0.09, 0.07, 0.06, and -0.15 in Lines H1, H2, L1, and L2, respectively. As correlated responses to the selection, male quail in the high lines were heavier, exhibited greater relative aggressiveness, and had larger cloacal glands than those of the control and low lines.

In vivo aromatization of [3H]testosterone in high and low mating lines of Japanese quail

Japanese quail selected bidirectionally for adult mating frequency were utilized to study in vivo aromatization of testosterone (T) in relation to masculine copulatory behavior. Functionally castrated high (HM) and low mating (LM) line quail were injected with 75 microCi of [3H]T. One hour after the injection, all radioactivity recovered in telencephalic-diencephalic brain tissue was in the form of T, dihydrotestosterone (DHT), or estradiol (E2). Neither the total 3H nor the [3H]T metabolite radioactivity differed between the two genetic lines. Of all [3H]T metabolic radioactivity, [3H]E2 represented 45 +/- 6 % in the HM line and 46 +/- 6% in the LM line, indicating that the line difference in mating frequency was not due to a corresponding difference in aromatase activity. Inasmuch as both the HM and LM line birds actively converted T to E2, these results implicate a neural mechanism involving E2-receptor interactions as the cause of the behavioral differences between the HM and LM lines.

Genetics of lipid deposition in the Japanese quail

The research presented here was designed to investigate the mode of inheritance of fat and lean tissue deposition, and the relationship between them and body weight in Japanese quail. Heterotic effects were found for weight, size, and number of adipocytes in the abdominal fat depots, weight of the sartorial fat depot and percentage carcass fat with means for the hybrids being lower than those for the parental lines. General inferences concerning the importance of nonadditive genetic variation for lean and body weight were precluded due to inconsistencies observed among mating combinations. Thus, although heterosis and recombination effects were general for characteristics associated with fat deposition, the situation for body weight and lean was unique to the populations involved. It may be hypothesized that heterosis in the efficiency of feed utilization is reflected by the heterosis for fat deposition which explains why hybrids utilize feed better than their parental lines.

The effects of exogenous steroidal hormones on the testes of quail from selected high and low mating lines

Several steroid hormones were tested for their effects on the testes of lines of Japanese quail selected for high and low mating frequency. Estradiol benzoate and testosterone propionate caused a complete and partial regression of the testes, respectively, while dihydrotestosterone did not affect testicular weight. Spermatogenesis was adversely affected by both estradiol benzoate and testosterone propionate but not by dihydrotestosterone. Dihydrotestosterone caused a significant increase in the diameter of the seminiferous tubules while estradiol benzoate and testosterone propionate caused a significant decrease in tubular diameter. Significant line differences were found; the high mating line exceeded the low mating line for each of the treatments except extradiol benzoate. Extradiol benzoate caused testicular regression in both lines.

Reverse selection in a Japanese quail line previously selected for 4-week body weight

After 38 generations of individual selection for high 4-week body weight in a Japanese quail line (T) fed a 20% protein diet containing .2% thiouracil, a reverse selected line (TR) was established by selecting quail in the T line with the lowest 4-week body weight. The TR line was thereafter provided with the same nutritional environment as the T line and selected for low 4-week body weight for 5 generations. The mean 4-week body weights of T line quail increased only slightly from generation 38 through 43. The 4-week body weights of the TR line, however, showed a definite downward trend. The difference in 4-week body weight between the T and TR lines in generation 43 was 15.2 g.