Paul F. Nicoletto

SPATIAL SCALING OF SPECIES COMPOSITION: BODY MASSES OF NORTH AMERICAN LAND MAMMALS

We describe the nonrandom assembly of the North American terrestrial mammalian fauna based on body size and spatial scale. The frequency distribution of body masses among species for the entire continental fauna was highly modal and right skewed, even on a logarithmic scale; the median size of the 465 species was approximately 45 g. In contrast, comparable frequency distributions for 24 small patches of relatively homogeneous habitat were essentially uniform, with approximately equal numbers of species in each logarithmic size class; the median sizes of the 19-37 species ranged from approximately 100 to 2,500 g. Frequency distributions for 21 biomes (large regions of relatively similar vegetation) were intermediate between the continental and local assemblages. This pattern of assembly indicates that species of modal size (20-250 g) tend not to coexist in local habitat patches and they replace each other more frequently from habitat to habitat across the landscape than species of relatively large or small size. We hypothesize that three mechanisms are necessary and possibly sufficient to produce this result: competitive exclusion of species of similar size within local habitats, differential extinction of species of large size with small geographic ranges, and greater specialization of modal-sized species owing to energetic and dietary constraints.

Female choice in the guppy (Poecilia reticulata): the interaction between male color and display

Abstract. The effect of two components of male courtship, color and display behavior, on female choice of mates was investigated in the guppy (Poecilia reticulata). Computer-modified videos were constructed to determine the relative importance of a static trait, the presence or absence of carotenoid pigment (C and NC), and a dynamic trait, high and low display rate (HD and LD), on female response. Females were given a choice between all combinations of male display and color in a binary choice design. Preference was determined by the time females spent visually inspecting the animation. Females preferred animations with high display rates when both animations displayed color (CHD vs CLD), but not in the absence of color (NCHD vs NCLD). Equal numbers of females chose the color/low-display animation and the no-color/high-display animation when the two were paired. Conversely, color became a criterion of choice when both animations showed a low display rate (CLD vs NCLD), but not when both displayed at a high rate (CHD vs NCHD). These results suggest that females use both static and dynamic traits to evaluate males, but their rankings are affected by the choices available. Results of these experiments provide insights into how females use multiple traits to assess males.

Age and Experience Affect Female Choice in the Guppy (Poecilia reticulata)

Female choices of males, and how these choices are influenced by ecological and social factors, have been studied extensively. However, little is known about the effects of age and breeding experience on female mating decisions. We used video techniques to examine female mate choice in guppies based on the area of carotenoid (orange) pigmentation on the body. Females were presented with paired images of males, one ornamented and the other plain. Visual preference for each male was measured. Age‐related changes in the criteria of choice were examined by comparing the responses of the same mature but sexually inexperienced 6‐mo‐old and 12‐mo‐old females. Effects of breeding experience on female choice were examined by comparing mate preferences of 12‐mo‐old female virgins with their preferences after they had mated and produced a brood. Female preferences for ornamented males with large areas of carotenoid pigment changed with age but not with mating experience. Six‐month‐old virgin females preferred ornamented males, whereas 12‐mo‐old virgin and postpartum females did not differentiate between males based on orange coloration. The results are discussed in light of life‐history theory and have important implications for studies of sexual selection as well as for the design of mate‐choice studies.

Repeatability of female choice in the guppy: response to live and videotaped males

The degree to which females are consistent in their mate preferences has implications for studies of sexual selection. Because choice of females for particular males may be affected by temporal changes in male characteristics, consistency of mate preferences of individual females of Poecilia reticulata was studied by presenting them with the same male pairs in consecutive trials under three experimental procedures: live males behind clear glass, live males behind one-way glass and images of males on videotape. Although females did not habituate to males in any of the experiments, they spent significantly more time in proximity to males behind clear glass than in the video and one-way glass presentations. Females preferred the bright male over the pale one in the video and the clear glass presentations, but not in the one-way glass experiment. Repeatability of preferences by individual females for a male was high in the video and one-way glass presentations but low in the clear-glass experiment. Behavioural interactions with the male in the clear-glass experiment affected both the time that females spent viewing males as well as female visual preferences. Results indicate that the video playback is not only useful for detecting differences between female preferences for morphological traits of male guppies, but is also much more effective in detecting preferences than the other two techniques, because it eliminates temporal variation in male behaviour.

A polymorphism in female preference for a polymorphic male trait in the swordtail fish Xiphophorus cortezi

Xiphophorus cortezi males are polymorphic for the pigment pattern vertical bars. In this study, we determined whether X. cortezi females are polymorphic in their preference for this trait by examining both within- and between-individual variation in female preference. There was significantly more variation in female preference within than between individuals using both video animations and live males as stimuli; repeatability measures were 0.86 and 0.5, respectively. Some females had a strong preference for males with bars, some for males without bars, and some had either a weak preference or no preference at all. We also found a significant difference in the strength of preference for bars between females with and without bars, suggesting the potential for a genetic correlation between preference and trait. Finally, we examined female preference for bar symmetry in the same females tested for preference for bars. We detected a significant preference for bar symmetry in the population of females as a whole, and a positive relationship between the strength of this preference and a preference for the presence/absence of bars among the subset of females that preferred ‘no bars’. We discuss these results in light the possibility that these two preferences are interrelated. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

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 (7 sec vs. 2.3 sec), 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.

Consensus among females in their choice of males in the guppy Poecilia reticulata

Abstract We studied female guppies from two populations (Trinidad and Jemez Springs, New Mexico) to determine their mating preferences, the degree of consensus among females for particular male phenotypes, and the variation among females for the types of traits they prefer. We recorded the visual responses of 68 Trinidad and 10 Jemez females in paired male trials. The three sexually-selected male traits quantified were the area of orange color and iridescence on the body, and display behavior. Females from the Trinidad population agreed in their choice of males in three of the eight replicates, and this agreement was based on display rate rather than male color patterns. Females from the Jemez population showed no agreement in their preferences of males. Mating preferences of females varied both between populations and among females of a population. In both populations, female preferences were based primarily on courtship intensity and only secondarily on color pattern. However, females from both populations differed in the relative importance of orange color and iridescence. The fact that females differ in criteria for evaluating males has important implications for selection and maintenance of color polymorphisms and for the interactions among multiple secondary sexual traits of males in the guppy.

The role of sexual selection in the loss of sexually selected traits in the swordtail fish Xiphophorus continens

Swordtail fish have been studied extensively in relation to several exaggerated male traits that have evolved due to sexual selection. However, one species of swordtail fish, Xiphophorus continens, lacks all of these traits. Males in this species are relatively small, lack swords and do not possess any of the pigment patterns found throughout the swordtails and platyfish. In this study we compared the mating behaviour of X. continens to the mating behaviours of other swordtail fish to determine whether a relaxation of sexual selection may have played a role in the loss of large male size and the pigment pattern vertical bars. We found that X. continens lacked the courtship behaviours present in other swordtail species, and that female mating preference for male size and male response to the pigment pattern vertical bars were significantly weaker than in other swordtails we have tested. In addition, results of staged male–male interactions suggested that neither male size nor vertical bars are under strong selection due to male–male competition. However, we did detect a polymorphism in female preference for vertical bars, suggesting that the response of female X. continens to vertical bars has been evolutionarily retained even though the trait was lost. Based on what is known about female preference for body size and bars, and male response to body size and bars across the northern swordtails, we hypothesize that the loss of large male size was due to a relaxation of sexual selection, whereas the loss of vertical bars was not.

The relationship among swimming performance, courtship behavior, and carotenoid pigmentation of guppies in four rivers of Trinidad

In the laboratory, courtship behavior and carotenoid pigmentation of male guppies are condition-dependent traits, since their expression is affected by physical vigor and environmental factors such as water velocity and diet. Whether these relationships exist in guppies under field conditions is yet to be determined. We compared the swimming performance, courtship behavior, and carotenoid pigmentation of guppies from headwater and downstream localities in four rivers of Trinidad. Swimming performance and courtship behavior of males differed among rivers and between headwater and downstream sites. Guppies from headwater sites swam significantly faster and had higher display rates than those from downstream sites. Mean swimming performance across sites was positively correlated with mean water velocity, but was correlated with the number of orange color spots (carotenoid pigment) in only one river. These results indicate that the courtship behavior of Trinidadian guppies is condition-dependent because the amount of display behavior is positively correlated to swimming performance, a measure of physical endurance. The proximal cause for this condition-dependence may be predator induced variation in microhabitat use by guppies in headwater and downstream locations.

Courtship behavior, swimming performance, and microhabitat use of Trinidadian guppies

SynopsisWe document differences in the use of microhabitats, male courtship behavior, and swimming performance of populations from headwater and downstream sites in two rivers of the Oropuche drainage in Trinidad. Guppies from headwater sites used microhabitats with higher water velocities, had a higher swimming performance, and were less patchily distributed than guppies from downstream sites. Although males from the headwater and downstream sites had similar display rates, males from headwater sites displayed in microhabitats with higher velocities (riffles) whereas males in downstream sites courted in still pools. Subtle effects of female choice maintain the honesty of male courtship behavior in various microhabitats. In downstream sites, where predators impose a survivorship cost on ornamental males, swimming performance was positively correlated with area of carotenoid ornamentation. In headwater sites, males frequently displayed in fast-flowing water, thus paid a higher metabolic cost of courtship. Interactions between characteristics of the physical habitat and predation pressure not only affect the distribution of guppies, but also have subtle effects on the types of condition-dependent traits favored by females.