Josabel Belliure

European rabbits as ecosystem engineers: warrens increase lizard density and diversity

Mammals that build extensive open burrow systems are often classified as ecosystem engineers, since they have the potential to modulate the availability of resources for themselves and other organisms. Lizards may benefit from the heterogeneity created by these structures, especially if coupled with an increased offer of sites for refuge and thermoregulation. However, information about these engineering effects by burrowing animals is scarce. We investigated the influence of European rabbit burrows on several parameters of a Mediterranean lizard community (abundance, density, diversity and body condition) in three different habitats (open pastures, holm oak and scrub patches). We found that lizards were positively associated with burrows, and that burrows determined lizard presence at otherwise unfavourable habitats. Moreover, community parameters such as density and species richness were higher in sites with burrows. Burrows influenced lizard species in different ways, and were also relevant for other Mediterranean vertebrates, as revealed by questionnaires to experts. We also explored the possible resources provided by burrows for lizards. Warrens offer relatively abundant prey and appropriate retreat sites for refuge and thermoregulation. Warrens may have further implications within the ecosystem, acting as stepping stones, allowing lizards to reach otherwise inaccessible habitat patches. This study shows that European rabbit warrens have a positive influence on lizard density and diversity, and confirms the role of rabbits as ecosystem engineers. This reinforces the need for appropriate conservation measures for rabbits, especially given their threatened status in the Iberian Peninsula. Furthermore, our study highlights that taking into account the influence of engineering activities increases our awareness of species interactions, and may translate into more adequate conservation measures for the preservation of biodiversity.

The role of urban greenspaces in fauna conservation: the case of the iguana Ctenosaura similis in the 'patios' of León city, Nicaragua

Private urban greenspaces, called ‘patios’ in Latin America, can act as important refuges for wildlife in scattered growing cities of the tropics. We studied the presence and abundance of the black spiny-tailed iguana (Ctenosaura similis) in patios of León city (Nicaragua). Forty patios were structurally characterized and abundances of iguanas were determined through surveys of inhabitants supported by observations of specimens and burrows. Patio area and maximum tree height were variables positively related with presence and abundance of iguanas and presence of burrows. The permeability of fences for iguana movements and the presence of preferred trees for food were also related to presence and abundance of iguanas. Stepwise selection model for abundance of iguanas included number of preferred trees, maximum tree height and permeability of fences. The presence of iguanas was only explained by maximum tree height. Our results show that the indigenous-root types of patios offer the most adequate conditions for the establishment and maintenance of iguana populations among the studied cases. In the light of these results, management practices to preserve the Ctenosaura similis populations in urban patios are suggested.

Red tails are effective decoys for avian predators

The decoy or deflection hypothesis, which states that conspicuous colouration is present in non-vital parts of the body to divert attacks from head and trunk, thus increasing survival probability, is a possible explanation for the presence of such colouration in juveniles of non-aposematic species. To test this hypothesis we made plasticine and plaster lizard models of two colour morphs, red or dark-and-light striped tails, based on the colouration of spiny-footed lizard (Acanthodactylus erythrurus) hatchlings, which naturally show a dark-and-light striped dorsal pattern and red tail. Lizard models were placed in the field and also presented to captive common kestrels (Falco tinnunculus), a common avian lizard predator. The number of attacks and the body part attacked (tail or rest-of-body) were recorded, as well as the latency to attack. Our results suggest that models of both colour morphs were recognized as prey and attacked at a similar rate, but in the field, red-tailed models were detected, and thus attacked, sooner than striped-tailed. Despite this increase in detection rate by predators, red-tailed models effectively diverted attacks to the tail from the more vulnerable body parts, thus supporting the decoy hypothesis. Greater fitness benefits of attack diversion to the tail compared to the costs of increased detection rate by predators would explain the evolution and maintenance of red tail colouration in lizards.

Bill size in relation to position in the colony in the chinstrap penguin

-In most seabirds, breeding success can be related to the ability to obtain a suitable nest-site within the colony, and this may result in competition for the limited number of available sites. Thus, if nest-sites vary in quality, individuals of the same sex are expected to compete for access to the highest quality nest-sites to enhance their own fitness. It is therefore expected that intrasexual competition would result in a correlation between size in the competing sex, or the size of a trait used as a weapon, and nest quality. Chinstrap Penguins (Pygoscelis antarctica) fight with other conspecifics using the bill as a weapon. If bill size provides an advantage for intra-specific combat, we would expect stronger bills in males occupying the best nest sites. We studied patterns of some adult morphological traits in relation with nest position in a colony of Chinstrap Penguins. Bill morphology was related to nest position in the colony, with individuals occupying the central positions having the deeper bills. This relationship was found in both sexes. Our data suggest that competition for position within the colony is not an important factor involved in the sexual dimorphism shown by the Chinstrap Penguin. Received 31 August 2000, accepted 1 October 2000.

Phylogenetic relationships of Isospora, Lankesterella, and Caryospora species (Apicomplexa: Eimeriidae) infecting lizards

In this study, several species of Isospora infecting lizards were genetically characterized. Specifically, five described and four newly described species of Isospora were included in a phylogeny of the family Eimeriidae. These species were isolated from hosts originally inhabiting all geographic continents except Europe. Phylogenetic analyses of the 18S ribosomal RNA (rRNA) gene grouped these nine species of Isospora with Lankesterella species and Caryospora ernsti. Therefore, within this clade, different evolutionary strategies in oocyst development and transmission occurred. Although the characteristic endogenous oocyst development of the genus Lankesterella may have arisen only once, the reduction in the number of sporocysts observed in the genus Caryospora occurred at least twice during coccidian evolution, as evidenced by the phylogenetic position of Caryospora bigenetica as the sister taxon of the group formed by reptilian Isospora, Lankesterella, and C. ernsti. Within this group, C. ernsti was the sister taxon to the genus Lankesterella. Overall, our results contradict the proposed monophyly of the genus Caryospora, highlighting the need for a thorough taxonomic and systematic revision of the group. Furthermore, they suggest that the recent ancestor of the genus Lankesterella may have been heteroxenous.

Exploring the function of red colouration in female spiny-footed lizards (Acanthodactylus erythrurus): patterns of seasonal colour change

In spiny-footed lizards (Acanthodactylus erythrurus), adult females (but not males) show conspicuous red colouration in the tail and hind legs. To investigate the function of this red colouring and proximal causes of seasonal colour change, we captured adult females before the reproductive season and kept them in captivity in one of the three following situations: with a male and fertilization possible, with a male and fertilization impossible, or with another female (fertilization also impossible). Colour was quantified using spectrophotometry. Red colouration increased shortly before the onset of reproduction, but faded during the breeding season and became whitish (light buff-gray) in all cases. Both fertilized and unfertilized females laid eggs or were gravid after two months of the experiment, but while fertilized females laid mostly fertile eggs, unfertilized females only laid infertile eggs. Both egg formation and colour change might be triggered by abiotic factors, although female characteristics also play a role, since heavier females changed colour and laid eggs earlier. Females interacting freely with a male were darker at the end of the breeding season than females separated from the male, indicating that fertilization or physical contact might also have an effect on colouration. Colour change patterns found in this study suggest that female red colouration might have a mating-related function, but do not support a courtship rejection function for the red colour. However, whitish colouration resulting from red fading might signal gravidity in this species. Future experimental manipulation of female colouration will be needed to test these hypotheses.

Red coloration in juvenile spiny-footed lizards, Acanthodactylus erythrurus, reduces adult aggression

In many animal taxa, coloration is a visual signal used for communication among conspecifics, for example between age classes. Juvenile coloration has been hypothesized to reduce aggression from adults in some species, in what is called the aggression avoidance hypothesis. Spiny-footed lizards are good subjects for testing this hypothesis, as juveniles develop conspicuous red coloration on their hind limbs and tails that fades in adulthood. To test the influence of juvenile coloration on adult aggressiveness, we conducted videotaped encounters in captivity between adults of both sexes and juveniles with their natural red coloration, or experimentally painted either red or white on their natural red parts. Then we recorded the number of times juveniles were bitten and attacked. In unpainted juveniles, no significant relationship was found between juvenile coloration (brightness, red chroma or hue) and adult aggressiveness. However, juveniles painted red were bitten less than those painted white when number of times bitten was controlled for number of times attacked. This result supports the aggression avoidance hypothesis, as an escalation from low-intensity (attacking) to high-intensity aggression (biting) was less probable towards red juveniles. The presence of red coloration in juveniles caused the reduction in adult aggression, while small natural variations in this red colour did not seem to have any further effect. Juvenile red coloration in this species might indicate age or sexual immaturity to adults.

Parental physiological condition and reproductive success in chinstrap penguins (Pygoscelis antarctica)

Recent studies suggest that parental resource allocation may be the most important factor explaining differences in reproductive output among parents. That said at least two different hypotheses of balance between parental foraging effort and resource allocation have been proposed. First, parents with high foraging effort have high reproductive success. Second, parents with higher allocation of resources to offspring have high reproductive success. We tested the second hypothesis using chinstrap penguins (Pygoscelis antarctica) as a model. We evaluated nutritional condition of the parents using blood urea, uric acid, creatine kinase, and cholesterol levels. We evaluated reproductive success according to total mass of the brood and asymmetries inside the brood. We measured the degree of asymmetry using weight and culmen length. Generalized linear models were used to examine relationships between adult plasma urea levels with year, nest position, and degree of asymmetry in chicks. Our results demonstrate that lighter broods were more asymmetric and associated with lower values of adult plasma urea, uric acid, and creatine kinase. We interpret these findings as evidence that the birds allocate fewer resources to their chicks than adults with more symmetric broods are.

Coloration reflects skin pterin concentration in a red-tailed lizard

When integumentary tissue pigments are contained in chromatophores, tissue color might not depend exclusively on the amount of pigment. Whether coloration does or does not reflect pigment concentration may be very significant for intraspecific communication, for example when pigment concentration provides fitness-related information. We studied the pigment responsible for the orange/red ventral tail coloring in a lacertid lizard species (Acanthodactylus erythrurus), and whether the color was related to skin pigment concentration. The pigment was identified as a pterin, a higher concentration of which resulted in darker, more red-saturated, redder (less orange) ventral tail skin color. The dorsal tail integument, even though it appears mostly gray to the naked eye, also contained pterins, and furthermore, the dorsal and ventral pterin concentrations were positively correlated. A possible explanation for these results is that pterins accumulate in the skin of the whole tail, even if only needed in the ventral part, but are concealed in the dorsal part. In this way, ventral orange/red coloration would accurately reflect pterin concentration, which provides the basis for a signaling function, while dorsal coloration would become less conspicuous as an anti-predatory mechanism.

Fire benefits flower beetles in a Mediterranean ecosystem

Despite the abundance of plants that benefit from fire in Mediterranean ecosystems, little is known about the possible presence of fire-favoured insects (other than bark beetles). For two years we sampled invertebrates after two large wildfires in eastern Spain and demonstrate that two flower beetle species, Protaetia morio and P. oblonga (Cetoniidae), show a pyrophilous behaviour. These beetles were much more numerous after the fires than in unburnt plots around the fire perimeter; in addition, these species tended to increase in number with the distance from the fire perimeter and with fire recurrence, especially P. morio. These results were maintained for the two postfire years sampled. The results for the beetles do not support the hypothesis of postfire colonization, but that local populations survived the fire as eggs or larvae protected in the soil (endogenous persistence). We propose that the increase in population size (compared with unburnt zones) could be driven by the reduction of their predator populations, as vertebrates that feed on these beetles were disfavoured by fire. That is, the results suggest that these flower beetle species benefit from fire because fire disrupts antagonistic interactions with their predators (predation release hypothesis). Given the omnipresence of small mammals, soil insects, and fires, the processes described here are likely to be general but unexplored.