Preferences of female American goldfinches (Carduelis tristis) for natural and artificial male traits

We conducted two experiments to determine mating preferencesof female American goldfinches (Carduelis tristis). In the firstexperiment, females were allowed to choose among four naturallyvarying males. In the second, females chose among four maleswearing either orange, blue, yellow, or no color bands. In experiment1, females performed more courtship with males that had significantlybrighter bills and were brighter overall. In experiment 2, femalespreferred males wearing orange bands over unhanded males. Blue-bandedmales ranked second and yellow third, but neither was preferredsignificantly more often than the unbanded males. A female'spreference for a particular band color was weakly associatedwith her own bill and plumage measures; females with brighterthroat feathers and yellower bills preferred orange bands toblue bands. The results suggest that female preferences fororange and yellow may be functional and that females may alsohave aesthetic preferences.     

Intraspecific competition in Zabrotes subfasciatus: Physiological and behavioral adaptations to different amounts of host

Abstract The effects of competition on populations of the bean weevil Zabrotes subfasciatus were analyzed during 41 generations under different competition levels. Three competition environments were established by maintaining the number of couples (6) and varying the amount of available host seeds: HC, high (limited availability of host: 1.35 g); IC, intermediate (intermediate availability of host: 6 g); and LC, low competition (abundance of host: 36 g). It was found that the distribution of the eggs laid on grains was different among treatments: in LC, for example, although females showed high fecundity (35.4 ± 5.6 eggs/female) the number of eggs laid on each grain was small (1.2 ± 0.4 eggs on each seed), thus avoiding larval competition of their offspring; whereas in HC treatment, females showed low fecundity (27.04 ± 4.5 eggs/female) but laid many eggs on each grain (15.03 ± 4.3 eggs). There were no changes in the ability to respond to different amounts of host via oviposition behavior (egg distribution) during 41 generations. However, HC females had more offspring than LC females under HC conditions. This suggests that HC insects evolved toward higher fitness in crowded conditions. In addition, after inverting the competition level, insects behaved independently of the treatment conditions they experienced through generations, thus showing that oviposition behavior is flexible. Taken together, our results show that Z. subfasciatus presents a broad range of behavioral and physiological responses which allows for quick and reversible adjustments to sudden changes in the amount of resources.     

Female within-nest spawning-site preference in a paternal brooding blenny and its effect on the female mate choice

Female spawning-site preference within a nest and its effect on the female mate choice in a paternal brooding blenny Rhabdoblennius ellipes , were examined in rocky intertidal pools using artificial nests. The number of eggs deposited at the nest entrance site was lower than the number deposited at the center and at deep sites. Moreover, the within-nest difference in the egg developmental stage indicated that eggs at the nest entrance site were deposited after those at the center and deep sites. These results indicated that females prefer to spawn eggs in the center and deep sites rather than at the entrance site. Owing to the higher egg mortality rate at the entrance site, females may avoid spawning at such sites. An analysis of the nests in the study area suggested that the within-nest site preference affects female mate choice that is females avoided nests where only the entrance site was available for spawning and instead spawned in nests where the center and deep sites were available.     

The Use of Digitally-modified Videos to Study the Function of Ornamentation and Courtship in the Guppy, Poecilia reticulata

The use of video playback, digitally-modified video images, and animations is a potentially powerful tool for exploring the interactions between morphological and behavioral components of complex sexually selected traits. The utility of digitally-modified video was evaluated by the responses of females to male images in which either the behavioral components of display or the colors of ornamentation were manipulated. Females were presented with paired male images that varied only in the size of the orange or blue spot on the body (19.1% vs. 8.6%), courtship duration (7sec vs. 2.3sec), or courtship rate (3 displays min^-1 vs. 1 display min^-1). Females preferred male images with more vigorous courtship displays (both duration and rate) but did not discriminate between images differing in spot size. The results of the present study suggest that females discriminate more strongly between variation in male behavior than in their morphological attributes. The results of morphological manipulations should be interpreted with caution, however, because several factors could have contributed to the lack of female responses to color spot variation. Among them are lowered resolution of the computer image, which fails to capture the precision and complexity of the color pattern. Despite these potential difficulties, digitally-modified video promises to be a powerful method to study complex visual communication systems, where the function of and interaction between the various morphological and behavioral components is as yet poorly understood.     

EGG MORPHOLOGY AND OVIPOSITION PATTERNS OF THE STRO-BILOMYIA SPP. (DIPTERA: ANTHOMYIIDAE) FLIES DAMAGING SIBERIAN LARCH CONES IN NORTHEASTERN CHINA1)

Abstract The oviposition patterns of 6 larch cone flies, Strobilomyia spp., were surveyed in 1993 in Da Hinggan Mountains, northeastern China. The colonization of distinct phases of cone development and the selection of different sites to lay eggs allowed to distinguish 5 patterns of oviposition. Observations of the egg morphology and of the chorion architecture using scanning electron microscope lead to classify the examined cone fly eggs into 6 different types. Each type of egg was related to a given oviposition pattern. Among the 6 egg types, eggs of S. laricicola, S. melaniola and S. infrequens were identified with certainty. Although hypotheses were given, further experiments under controlled conditions are required to identify which of the 3 other egg types is associated to S. baicalensis, S. svenssoni and S. sanyangi, respectively.     

Egg-laying tactic in Phyllomorpha laciniata in the presence of parasitoids

Female insects are expected to choose oviposition sites that have the best conditions for offspring development and survival. Natural enemies, such as predators and parasitoids, may have a strong influence on the selection of oviposition substrates by phytophagous insects. The golden egg bug, Phyllomorpha laciniata (Villers) (Heteroptera: Coreidae) has an unusual reproductive strategy. Females mainly use conspecifics, both males and other females, as egg-laying substrates, but occasionally they oviposit on plants as well. Survival of the eggs is higher when eggs are carried by conspecifics than when they are laid on plants, due to predation and parasitism. We investigated egg-laying behavior in the forced presence of the egg parasitoid Gryon bolivari (Giard) (Hymenoptera: Scelionidae). Specifically, we studied whether females provide egg protection by avoiding oviposition under the risk of egg parasitization. We expected a lower oviposition rate under parasitoid presence, and the eggs, if any, to be placed preferably on conspecifics and not on plants, thus ensuring higher survival of the progeny. The results show that P. laciniata 's egg-laying rate was lower when they were enclosed with parasitoids than when parasitoids were absent, especially when plants were the only substrate to oviposit on. Moreover, females showed strong preference for laying eggs on conspecifics rather than on plants. Egg-laying in P. laciniata appears to be not only influenced by the availability of conspecifics, but also by the presence of egg parasitoids. This indicates that females may be able to detect G. bolivari and avoid oviposition when parasitoids are present. We discuss the possibility of conspecifics as enemy-free space.     

Parallel Evolution,not Always so Parallel: Comparison of Small Benthic Charr, <Emphasis Type=\"Italic\">Salvelinus alpinus</Emphasis>, from Grímsnes and Thingvallavatn,Iceland

Synopsis Iceland is unique in terms of geologically young freshwater systems and rapid adaptations of fresh water fishes to diverse habitats, e.g. lava with ground water flow. Iceland has six species of freshwater fishes, including Arctic charr, Salvelinus alpinus. Previous research has shown great diversity within this species. Four different morphs of Arctic charr are found in one lake, Thingvallavatn, including a small benthivorous charr. Similar populations of small benthic charr are known from several other Icelandic freshwater locations, including Nautavakir in Grímsnes. Our comparison of the small benthic charr morphs in Thingvallavatn and in Grímsnes showed that they are similar in morphology but distinguishable in several characteristics. Small benthic charr in Grímsnes and Thingvallavatn demonstrate similar adaptations and are an example of parallel evolution. However, subtle morphological differences between them indicate further specialized adaptations at each location.     

Evidence for the signaling function of egg color in the pied flycatcher Ficedula hypoleuca

A recent hypothesis proposes that the bright colors, especiallyblue and green, of many avian eggs may function as signals offemale or offspring phenotypic quality or condition to malesin species with biparental care, inducing them to allocate moreeffort to their offspring. The pigment determining blue andgreen egg colors is an antioxidant whose availability for eggshellcoloring may be limited. To test the signaling function on aspecies with blue eggs, the pied flycatcher Ficedula hypoleuca,we measured egg color with a spectrophotometer on the day oflaying and obtained two principal components from their reflectancespectra that together explained 99% of variation and representedshell lightness, and hue and saturation, respectively. We alsomeasured female immunocompetence during the nestling periodthrough the response to phytohemagglutinin as a measure of cell-mediatedimmunity and the response to a tetanus vaccination as a measureof humoral immunity. The total amount of immunoglobulins inblood of females and of nestlings before fledging was also estimated.Mean within-clutch egg darkness was positively associated withboth measures of female immunocompetence, while better femalecondition was associated with colors tending away from intermediateand toward short wavelengths. Ageing female laid lighter eggs.The mean within-brood level of nestling IgY was also associatedwith mean within-clutch egg colors tending away from intermediateand toward short wavelengths. Mean egg darkness decreased linearlyduring the laying sequence, suggesting pigment limitation. Maleswere observed frequently visiting nests during the laying period,allowing them to observe eggs before the start of incubation.These results support the signaling hypothesis for explainingbright colors of avian eggs.