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.      

Defining Vertical Bars in Relation to Female Preference in the Swordtail Fish Xiphophorus cortezi (Cyprinodontiformes, Poeciliidae)

Defining a male trait in relation to female preference is an important step towards determining the role that female preference has played in the evolution of a male trait. The pigment pattern 'vertical bars' is a complex male trait that functions as a sexual signal in swordtail fishes. A previous study suggested that X. cortezi females had a preference for males with more vertical bars. In that study, however, bar number had been reduced on the stimulus males by removing the most posterior bars, which changed the distance over which the bars spanned, in addition to changing bar number. To determine whether X. cortezi females have a preference for greater bar span and/or number of bars, we tested for female preference in two experiments. First, we gave females a choice between males with a greater bar span or a smaller bar span, holding bar number and total pigmented area constant. Females spent significantly more time with the males with the smaller bar span. This result, together with results from the previous study, suggest that females do not assess bar span alone, but possibly a composite component of the bars, such as bar frequency (number of bars/bar span). Secondly, we gave females a choice between six thinner bars or one wider bar of equal pigmented area. The six-bar treatment had a greater bar span in addition to more bars. We detected no preference for either treatment. These results suggest that the previously detected preference for more bars may actually reflect a preference for greater pigmented area. Finally, we present data on natural variation in the bars for X. cortezi and use principal components analysis to provide a composite definition of this trait.     

Further examination of female preference for vertical bars in swordtails: preference for 'no bars' in a species without bars

Xiphophorus pygmaeus males do not have a vertical bar pigment pattern and so female preference for the bars was determined by giving females a choice between pairs of X. multilineatus males without bars (all bars removed by freeze-branding) and with bars (freeze-branded between the bars). Female X. pygmaeus had a significant preference for male X. multilineatus without bars over males with bars, and this preference was significantly different from the preference for bars detected in X. nigrensis and X. multilineatus . The implications of the results are discussed in regard to models for the evolution of female preference.     

A linear model for symmetric receptive fields: implications for classification tests with flashed and moving images

The purpose of this study was to explore the effects of spatial and temporal properties on the expected responses of visual neurons that have linear receptive fields (RFs), particularly those having a mirror symmetric distribution of spatial subregions. Receptive fields that are symmetric in at least one spatial dimension occur in neurons of the retina, the lateral geniculate nucleus (LGN), and the visual cortex of mammals. Responses to flashing bars, moving bars, and moving edges were studied for different configurations of an analog RF model in which spatial and temporal aspects were varied independently. Responses of the model at intermediate stimulus speeds were found to agree with responses in the literature for X and Y units of the LGN and often for simple units of the visual cortex. In particular, having separated regions of response to light and dark edges, an identifying property of simple cells, was found to be a linear consequence of RF regions responding inversely to stimuli of opposite polarity. Model differences from responses of cortical complex units show that a linear model cannot mimic their responses, and imply that complex units employ major nonlinearities in coding image polarity (light vs dark), which signifies a nonlinearity in coding intensity. Because sudden flux changes inherent in flashing bars test mainly temporal RF properties, and slowly moving edges test mainly spatial properties, these two tests form a useful minimal set with which to describe and classify RFs. The usefulness of this set derives both from its sensitivity to spatial and temporal variables, and from the correlation between the linearity of a cell's processing of stimulus intensity and its RF classification.     

Illusory boundary interpolation from local association field

We previously showed that interpolation between vertically misaligned luminance edges of same polarity of contrast is preferred to that between co-linear edges of opposite polarity of contrast, although it results in illusory tilt (Roncato and Casco, 2003). We here analyze the spatial conditions that produce this illusory binding of vertically misaligned edges of light and dark tiles, alternated in a row, and in counterphase with those in the rows above and below. We find that, independently of scale and number of tiles in a row, the illusion is perceived when the vertical misalignment of more than three tiles is smaller than or equal to 9' and the horizontal separation between co-linear edges is smaller than or equal to 13'. These short distances suggest that the underlying mechanism is local. Both our phenomenological and psychophysical results support the notion of a local short-range association field, selective to contrast polarity, which produces a binding solution different from that of a phase-independent long-range mechanism. We suggest that the occurrence of the illusion at local-level is a result of the activation, within a local short-range association field, of units with orientation different from that stimulated by the physical edges. These units are not inhibited when they are close, iso-oriented and co-linear, and the misaligned edges from which they propagate have the same contrast polarity. We found that horizontal and vertical spatial limits for the interpolation covary but not such that their ratio is fixed, indicating that the two edges can be connected by projections having a relatively wide range of orientations.     

Visual resolution of the orientation cue by the honeybee (Apis mellifera)

Bees were trained to discriminate between a pattern with two or more black bars and a similar pattern with the bars at right angles. Earlier measures of the resolution of oblique black and white regular gratings of different periods were confirmed. The positions of the training bars were shifted every 5 min to prevent the bees from using their locations as cues. To measure the length of the detectors of edge orientation, the trained bees were tested with targets filled with parallel short black/white edges of various lengths. The minimum individual length of edge required to discriminate the orientation cue was found to be near 3 degrees, and similar for vertical, horizontal and oblique edges. This is the first time that this kind of resolution has been measured in an invertebrate. The bees learn and recognize the edge orientation, not the lay-out of the pattern.     

The preferences of the honeybee (Apis mellifera) for different visual cues during the learning process

By working with very simple images, a number of different visual cues used by the honeybee have been described over the past decades. In most of the work, the bees had no control over the choice of the images, and it was not clear whether they learned the rewarded pattern or the difference between two images. Preferences were known to exist when untrained bees selected one pattern from a variety of them, but because the preferences of the bees were ignored, it was not possible to understand how natural images displaying several cues were detected. The preferences were also essential to make a computer model of the visual system. Therefore experiments were devised to show the order of preference for the known cues in the training situation. Freely flying bees were trained to discriminate between a rewarded target with one pattern on the left side and a different one on the right, versus a white or neutral target. This arrangement gave the bees a choice of what to learn. Tests showed that in some cases they learned two or three cues simultaneously; in other cases the bees learned one, or they preferred to avoid the unrewarded target. By testing with different combinations of patterns, it was possible to put the cues into an order of preference. Of the known cues, loosely or tightly attached to eye coordinates, a black or blue spot was the most preferred, followed by strong modulation caused by edges, the orientation of parallel bars, six equally spaced spokes, a clean white target, and then a square cross and a ring. A patch of blue colour was preferred to yellow.     

Vertical bars on male Xiphophorus multilineatus: a signal that deters rival males and attracts females

We examined the function of the vertical bar pattern on maleswordtails (Xiphophorus multilinneatus) as a signal in bothmale-male competition and female choice. This pattern had previouslybeen described as an aggressive signal because males intensifiedthe bars during male-male encounters in the laboratory. Ourfield observations supported this observation and also showedthat bars intensified when males courted females. The intensityof bars was correlated with access to females in the field.Within the size range of males that have bars, however, neitherbar number nor male size appeared to influence access to females.We used freeze-branding to remove the bars from males in thelaboratory so that we could control for characters correlatedwith bar intensity, and tested males and females separatelyso that we could separate the influence of these two componentsof sexual selection. We compared the responses of males andfemales to males that had their bars removed and control malesfreeze-branded between the bars. Test males responded more aggressivelyto males without bars as compared to control males. In addition,females showed a preference for control males over males thathad their bars removed. These results suggest that the barsmay function as a signal that deters rival males and attractsfemales.     

Macrofaunal Responses to Edges Are Independent of Habitat-Heterogeneity in Experimental Landscapes

Despite edges being common features of many natural habitats, there is little general understanding of the ways assemblages respond to them. Every edge between two contrasting habitats has characteristics governed by the composition of adjoining habitats and/or by the nature of any transitions between them. To develop better explanatory theory, we examined the extent to which edges act independently of the composition of the surrounding landscape and to which transitions between different types of habitats affect assemblages. Using experimental landscapes, we measured the responses of assemblages of marine molluscs colonising different experimental landscapes constructed with different compositions (i.e. different types of habitats within the landscape) and different types of transitions between habitats (i.e. sharp vs gradual). Edge effects (i.e. proximity to the edge of the landscape) were independent of the internal composition of experimental landscape; fewer species were found near the edges of landscapes. These reductions may be explained by differences in differential larval settlement between edges and interiors of experimental landscapes. We also found that the sharpness of transitions influenced the magnitude of interactions in the different types of habitats in experimental landscapes, most probably due to the increased number of species in areas of transition between two habitats. Our experiments allowed the effects of composition and transitions between habitats to be disentangled from those of proximity to edges of landscapes. Understanding and making predictions about the responses by species to edges depends on understanding not only the nature of transitions across boundaries, but also the landscape in which the edges are embedded.     

All natural habitat edges matter equally for endangered <Emphasis Type="Italic">Maculinea</Emphasis> butterflies

An obvious consequence of habitat fragmentation is an increasing role of habitat edges for species survival. Recently it has been suggested that the endangered butterfly Maculinea nausithous prefers forested edges of its meadow habitats. However, the prevalence of forests in the study area used for this analysis makes it impossible to distinguish whether the effect detected is a genuine preference for forest edges or a preference for any natural patch edges as opposed to patch interiors. We investigated habitat selection by Maculinea nausithous and Maculinea teleius occurring sympatrically at five habitat patches surrounded by mosaic landscape. Butterfly capture positions were marked with GPS and subsequently analysed with GIS software. Both species avoided the interiors of their patches and concentrated in the edge zone, but these preferences were visible only at three larger patches exceeding 1 ha in area. Among different types of edges those bordering densely built-up areas were avoided, whereas all natural edges (adjacent to forests, reeds or grasslands) were similarly used. We hypothesise that preferences towards natural patch edges, regardless of their type, can be explained by the spatial interactions between Maculinea butterflies and Myrmica ants they parasitise. Patch surroundings constitute refuge space for the ants, and hence their densities may be expected to be higher near patch edges. Our findings indicate the importance of patch surroundings for the persistence of Maculinea populations. Regretfully, current legal framework makes it difficult to protect patch surroundings, where neither priority species nor their habitats occur.     

Larger swordtail females prefer asymmetrical males

Many organisms, including humans, find symmetry more attractive than asymmetry. Is this bias towards symmetry simply a by-product of their detection system? We examined female preference for symmetry of the pigment pattern vertical bars in the swordtail fishes Xiphophorus cortezi and Xiphophorus malinche. We found a relationship between preference for symmetry and female size, with larger and thus older females spending significantly more time with the asymmetrical video animation as compared to the symmetrical video animation. The preference for asymmetry we report demonstrates that even if females can detect symmetrical males better, this does not preclude subsequent selection on females to prefer symmetrical or asymmetrical males. In addition, because the preference was correlated with female size, past studies may have missed preference for either asymmetry and/or symmetry by not examining the relationship between female preference and size/age or by measuring a limited size/age distribution of females. In both of the species of swordtail fishes examined, a high proportion of males are asymmetrical by more than one bar. We suggest that female preference may be maintaining fluctuating asymmetries in these fishes.     

Performance data indicate summation for pictorial depth-cues in slanted surfaces

Over recent years much has been learned about the way in which depth cues are combined (e.g. Landy et al.. 1995). The majority of this work has used subjective measures, a rating scale or a point of subjective equality, to deduce the relative contributions of different cues to perception. We have adopted a very different approach by using two interval forced-choice (21FC) performance measures and a signal processing framework. We performed summation experiments for depth cue increment thresholds between pairs of pictorial depth cues in displays depicting slanted planar surfaces made from arrays of circular 'contrast' elements. Summation was found to be ideal when size-gradient was paired with contrast-gradient for a wide range of depth-gradient magnitudes in the null stimulus. For a pairing of size-gradient and linear perspective, substantial summation (> 1.5 dB) was found only when the null stimulus had intermediate depth gradients; when flat or steeply inclined surfaces were depicted, summation was diminished or abolished. Summation was also abolished when one of the target cues was (i) not a depth cue, or (ii) added in conflict. We conclude that vision has a depth mechanism for the constructive combination of pictorial depth cues and suggest two generic models of summation to describe the results. Using similar psychophysical methods. Bradshaw and Rogers (1996) revealed a mechanism for the depth cues of motion parallax and binocular disparity. Whether this is the same or a different mechanism from the one reported here awaits elaboration.     

Responses of epithelial and fibroblast-like cells to discontinuous configuration of the culture substrate.

The behaviour of epitheliocytes, their transformed analogues, and fibroblasts was studied on special culture substrates--lattices with large square openings (the area of an opening was 2000 microm2). It was shown that normal epithelocytes and fibroblasts initially attached to and spread on the lattice bars, were soon displaced into the lattice openings and appeared to be "sagged" in the substrate-free spaces. The cells remained attached to the bars only by their edges (epitheliocytes) or lateral processes (fibroblasts), whereas basal surfaces of the cells had no contacts with the substrate. Displacement of the cells from the bars into the lattice openings was observed only if during spreading the cell body was located on two perpendicular bars. In this position the cell body underwent bending which presumably induced stretching of the cell and its displacement into the opening. Unlike epitheliocytes, which gradually "covered" the lattice openings completely, the fibroblasts were retracted and elongated upon their displacement, "crossing" the openings by their bodies and processes. The epitheliocytes transformed by the ras oncogene and displaying a fibroblast-like shape, most often remained on the bars and were not displaced into the lattice openings. Induction of the epithelioid phenotype in fibroblasts by the agents, depolymerizing (colcemid) or disintegrating (taxol) the cytoskeletal system of microtubuli, was accompanied by a change in the behaviour of the cells: the treated fibroblasts, like epitheliocytes, acquired the ability to "cover" the lattice openings. Possible mechanisms of the cell reactions to the substrate having discontinuous configuration are discussed. It is supposed that these distinctions in reactions of epitheliocytes and fibroblast-like cells may result from different bending ability of the cells and/or differences between forces responsible for the cell adhesion to the lattice bars and forces stretching the cells over the lattice openings.     

A single pair of acidic residues in the kinase major groove mediates strong substrate preference for P-2 or P-5 arginine in the AGC, CAMK, and STE kinase families

Most basophilic serine/threonine kinases preferentially phosphorylate substrates with Arg at P-3 but vary greatly in additional strong preference for Arg at P-2 or P-5. The structural basis for P-2 or P-5 preference is known for two AGC kinases (family of protein kinases A, G, and C) in which it is mediated by a single pair of acidic residues (PEN+1 and YEM+1). We sought a general understanding of P-2 and P-5 Arg preference. The strength of Arg preference at each position was assessed in 15 kinases using a new degenerate peptide library approach. Strong P-2 or P-5 Arg preference occurred not only in AGC kinases (7 of 8 studied) but also in calmodulin-dependent protein kinase (CAMK, 1 of 3) and Ste20 (STE) kinases (2 of 4). Analysis of sequence conservation demonstrated almost perfect correlation between (a) strong P-2 or P-5 Arg preference and (b) acidic residues at both PEN+1 and YEM+1. Mutation of two kinases (PKC-theta and p21-activated kinase 1 (PAK1)) confirmed critical roles of both PEN+1 and YEM+1 residues in determining strong R-2 Arg preference. PAK kinases were unique in having exceptionally strong Arg preference at P-2 but lacking strong Arg preference at P-3. Preference for Arg at P-2 was so critical to PAK recognition that PAK1 activity was virtually eliminated by mutating the PEN+1 or YEM+1 residues. The fact that this specific pair of acidic residues has been repeatedly and exclusively used by evolution for conferring strong Arg preference at two different substrate positions in three different kinase families implies it is uniquely well suited to mediate sufficiently good substrate binding without unduly restricting product release.     

The tactile perception of stimulus orientation

Studies of the visual system suggest that, at an early stage of form processing, a stimulus is represented as a set of contours and that a critical feature of these local contours is their orientation. Here, we characterize the ability of human observers to identify or discriminate the orientation of bars and edges presented to the distal fingerpad. The experiments were performed using a 400-probe stimulator that allowed us to flexibly deliver stimuli across a wide range of conditions. Orientation thresholds, approximately 20 degrees on average, varied only slightly across modes of stimulus presentation (scanned or indented), stimulus amplitudes, scanning speeds, and different stimulus types (bars or edges). The tactile orientation acuity was found to be poorer than its visual counterpart for stimuli of similar aspect ratio, contrast, and size. This result stands in contrast to the equivalent spatial acuity of the two systems (at the limit set by peripheral innervation density) and to the results of studies of tactile and visual letter recognition, which show that the two modalities yield comparable performance when stimuli are scaled appropriately.     

Context‐dependent female preference for multiple ornaments in the bearded reedling

While it is well established that females prefer to mate with well‐ornamented males, the influence of perceptive and cognitive processes on the expression of female mate choice is still poorly known. It has been suggested that the female perception of a male's attractiveness is not absolute, but depends on the other males with which he is compared that have been previously encountered (comparative evaluation). We investigated whether mate preference in bearded reedlings (Panurus biarmicus) is dependent on or independent of social context in relation to two different traits: beard and tail lengths. Each female had a choice between two to three males with different modifications of beard and tail. For each female, three different experiments were conducted (one binary and two trinary tests). We found that when females are presented with options that vary antagonistically with respect to two ornaments (binary test), some individuals prefer one trait while others the other trait. This indicates that in our bearded reedlings population exists a mate preference polymorphisms. Moreover, we found that the presence of a third stimulus, irrespective of the initial preference, reduced the strength of the initial preference – what we can call a “preference dilution effect.” Our results suggest that the female's choice may be constrained by her cognitive abilities when she is simultaneously presented with several options varying for two uncorrelated traits.     

Biogeographical zonation of African hornbills and their biotic and geographic characterisations

We studied the geographic ranges of the 23 African hornbill species using countries as distribution units, to search for either groups of similar distributions (chorotypes) or gradual replacement of species as two different types of distribution patterns. We used a probabilistic classification method to distinguish between these two types of biogeographic patterns. Then we analysed the influence of climate, area, surface covered by different types of habitat, and human disturbance in each country, as well as biotic features of the species involving the habitat preference, feeding requirements and habits, body size, sexual dimorphism, and metabolic parameters, on the biogeographic patterns detected. We found that 20 species were significantly classified into three chorotypes. The western-central chorotype comprises nine species characterised by their preference for forest habitat and their low sexual body mass dimorphism. These species occur in 25 countries, characterised by their low range of temperatures. The eastern chorotype includes three species characterised by their preference for feeding on the ground and greater dimorphism in mass between the sexes. Seven countries, characterised by their high values of savanna and grassland surface area, constitute the geographic element of this chorotype. The southern chorotype involves the distribution of eight species characterised by their preference for montane and coastal forests or woodlands. Eighteen countries fall into this chorotype and are characterised by their low values of temperature in the coldest month and greater surface area of desert scrub and desert forest. The other three species replace each other mainly following a gradual pattern within the study area.     

Amerindian (but not African or European) ancestry is significantly associated with diurnal preference within an admixed Brazilian population

Significant questions remain unanswered regarding the genetic versus environmental contributions to racial/ethnic differences in sleep and circadian rhythms. We addressed this question by investigating the association between diurnal preference, using the morningness–eveningness questionnaire (MEQ), and genetic ancestry within the Baependi Heart Study cohort, a highly admixed Brazilian population based in a rural town. Analysis was performed using measures of ancestry, using the Admixture program, and MEQ from 1,453 individuals. We found an association between the degree of Amerindian (but not European of African) ancestry and morningness, equating to 0.16 units for each additional percent of Amerindian ancestry, after adjustment for age, sex, education, and residential zone. To our knowledge, this is the first published report identifying an association between genetic ancestry and MEQ, and above all, the first one based on ancestral contributions within individuals living in the same community. This previously unknown ancestral dimension of diurnal preference suggests a stratification between racial/ethnic groups in an as yet unknown number of genetic polymorphisms.