1) What is the significance of the maternal half-sib design in Welch et al. for
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1) What is the significance of the maternal half-sib design in Welch et al. for the interpretation of the experiments?
Call Duration as an Indicator of Genetic Quality in Male Gray Tree Frogs Allison M. Welch, Raymond D. Semlitsch, H. Carl Gerhardt The "good genes" hypothesis predicts that mating preferences enable females to select mates of superior genetic quality. The genetic consequences of the preference shown by female gray tree frogs for long-duration calls were evaluated by comparing the performance of maternal half-siblings sired by males with different call durations. Off- spring of male gray tree frogs that produced long calls showed better performance during larval and juvenile stages than did offspring of males that produced short calls. These data suggest that call duration can function as a reliable indicator of heritable genetic quality The "good genes" model of sexual selec- through increased fitness of offispring. This tion predicts that some attributes of male prediction can be tested by evaluating the c courtship displays advertise genetic quality. relato between paternal call duration and Q Preferences for such attributes should allow the genetic quality of offspring females to mate with high-quality malesM gray tree frog advertisement calls and thereby benefit indirectly through en consist of rapidly repeated pulses. In dense hanced quality of offspring (1). Although choruses and in response to playbacks, males the good genes hypothesis has been tested tend to increase call duration by increasing several times (2), few studies have provided the number of pulses per call (11, 12). None- direct genetic evidence support ing this hy- theless, some males consistently produce pothesis (3). Only one such study involved longer calls than others in the same acoustic a species in which females cannot benefit environment (7, 12-14). Although long directly from their choice of mates (4). calls are usually produced at slow rates, Because selection for direct benefits such as thereby keeping aerobic metabolic costs rel- courtship feeding or parental care should atively constant (11, 14), males that produce overwhelm any selection for indirect (ge- ong calls spend less time calling per night netic) benefits (5), the role of good genes (11) and attend fewer choruses per season selection in the evolution and maintenance (8) than males that produce short calls. LongS of female preferences is best tested in spe calls thus appear to impose higher nonaero- cies in which females do not benefit directly bic costs than short calls. Call duration may from mate choice. therefore, be an honest indicator of male Female gray tree frogs (Hyla versicolor) genetic quality strongly prefer male advertisement calls of We tested whether call duration indicates long duration in laboratory experiments (6, heritable genetic quality by using maternal 7). In the field, females freely initiate mat- half-siblingships (half-sibships) to compare ings with calling males and do not always the performance of different males' off choose the first male encountered (7). Be spring while experimentally controlling for cause males do not defend oviposition sites almaternal effects. Maternal half-sibships offer nuptial gifts, or contribute parental care were generated by artificially crossing each (8, 9), and no difference has been found in female with two males that had been giv- fertilization success as a function of call du- ing calls of distinctly different durations in ration (10), there are no apparent direct he same social environment (Table 1) benefits of a female's mate choice. We there- Thus, within each maternal half-sibship, fore predicted that females selecting mates one sibship was sired by a male with calls of with long calls should benefit indirectly duration than the male siring the other sibship. Because call duration varies with chorus density, males' calls must be assessed in the same social context in order . Thus, in 1995 we selected nine sets of two males that had Division of Biological Sciences, University of Missouri Columbia, MO 65211, USA To whom correspondence should be addressed. E-mait: to be validly compared E VOL. 280 19 JUNE 1998 www.sciencemag.orgExplanation / Answer
1)In maternal half-sib design,maternal genetic contributions and maternal effects remains the same in all the study subjects and they vary only in the paternal genetics. This helps to relate the differences in observed phenotypes to differences in paternal genetic contribution, in H. versicolor.
2)Good gene hypothesis states that some attributes of male courtship displays announces their genetic quality and female mating preferences for those attributes help them to generate genetically superior offspring with those males. Here in this paper it is proven that the female's preference over the quality-long call duration is of no direct benefit to the female. The males are not found to defend oviposition sites, give nuptial gifts or participate in parental care- all of these proves that female's preference over long call duration is of no direct benefit to her. But it is actually indirectly helping her to produce genetically superior larvae and tadpoles.
Same female gives rise to offsprings of a male with long call duration and that of a male with short call duration. And it was observed that offspring of males with long duration calls always performed significantly better than or equal to offspring of males with short calls. This trend was seen in maternal half-sibs grown in favourable and unfavourable enviornmental conditions. These results show that female's preference on males with long call duration even though did not benefit her directly, it did help in producing genetically superior offsprings who shows better performance, which is in accordance with good gene hypothesis.
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