Control social del atractivo en un sistema de elección de pareja basado en un sesgo estético

[spa] En la naturaleza observamos individuos que se comunican honestamente con otros aun cuando el engaño parece la opción más ventajosa. Esta tesis estudia mediante qué mecanismos la comunicación honesta se mantiene en uno de los escenarios donde más esperaríamos la corrupción del sistema por parte de los emisores: la elección de pareja basada en un sesgo estético por parte de las hembras. Bajo este escenario, los machos, que resultan atractivos a las hembras porque expresan aquellos caracteres sexuales que satisfacen un sesgo estético preexistente. En esta tesis se estudia un mecanismo, al que llamamos “control social del atractivo”, en el que son los propios machos quienes velan por que sus competidores no expresen un atractivo mayor del correspondiente a su calidad. Este control se llevaría a cabo mediante un incremento de los episodios agonísticos que un macho deshonesto sufriría. La existencia de este mecanismo se ha estudiado en el portaespada Xiphophorus hellerii, un actinopterigio de la familia de los pecílidos. Los machos de dicha especie expresan un carácter intersexual, la espada, consistente en una prolongación de los radios inferiores de la aleta caudal. Dicho carácter parece explotar un sesgo presente en las hembras a favor de los machos de mayor tamaño aparente. Sin embargo, la espada se expresa honestamente ya que existe una correlación positiva entre el tamaño del cuerpo y la longitud de la espada. En consecuencia, debe existir algún mecanismo que prevenga que los machos expresen un espada más larga de la que le correspondería según su tamaño. En el primer capítulo, se testa la existencia de los comportamientos que los machos deberían expresar para que pudiese existir un control social del atractivo eficaz. En un primer experimento se demuestra que los machos de portaespada, al presentarles dos intrusos, tienden a atacar al más atractivo, el de espada más larga, cuando existe una diferencia de atractivo entre intrusos suficiente. Esta conducta la denominamos “intolerancia al atractivo”. En un segundo experimento de este mismo capítulo, se observa como la intolerancia al atractivo es ejercida por los machos dominantes hacia los subordinados. Así, sólo los machos dominantes, que también son los de mayor tamaño, pueden expresar las espadas más largas sin sufrir un incremento en el número de episodios agonísticos sufridos. El segundo capítulo de la tesis se dedica a comprobar cuáles son los costes asociados al ser agredido y derrotado. En el primer experimento de este capítulo se demuestra que los machos recuerdan y compiten por monopolizar aquellas zonas donde hubo hembras de tal manera que los machos agredidos y derrotados son expulsados de dichas zonas. En consecuencia, parece existir un coste intrasexual asociado a la derrota. Además, el segundo experimento del capítulo evidencia que las hembras prefieren a aquellos machos que han visto vencer, lo que implica un coste intersexual asociado a la derrota ya que un macho perdedor pierde atractivo frente las hembras. En el último capítulo se desarrollan una serie de simulaciones para ilustrar la lógica subyacente al control social del atractivo. Estas simulaciones muestran que la intolerancia al atractivo es una estrategia que desplazaría la estrategia original de agredir al azar y que una vez fijada en la población provocaría una asociación positiva entre calidad y atractivo de los machos. En definitiva, las experiencias realizadas sugieren que la espada es una señal intersexual cuya expresión honesta está garantizada por el control social del atractivo. Además, este mecanismo puede emerger evolutivamente como respuesta adaptativa a la expresión de cualquier señal intersexual potencialmente deshonesta independientemente del formato de dicha señal.[eng] This thesis focuses on how male-male competition could ensure the honest signaling of those intersexual traits that exploit female pre-existing biases by means of a mechanism called “social control of attractiveness”. We explored this possibility in the green swordtail (Xiphophorus hellerii) by testing whether male-male competition guarantees the body size-dependent expression of the sword, an intersexual trait displayed by males that fits a female pre-existing bias. In the first chapter of the thesis, I present two experiments in order to show that males actually express the required behavior that is expected to cause the social control of attractiveness. In the first experiment, I presented two intruder males to a resident male. The latter tended to direct its attacks towards the most attractive intruder when the difference in attractiveness between them was big enough. The second experiment showed that only small males suffered a punishment inflicted by large ones and that this punishment was associated to their attractiveness. The second chapter of the thesis shows that, following an attack, a defeated male suffers an intrasexual cost by losing access to females, as well as an intersexual cost owing to the fact that females prefer the winner of the contests that they eavesdrop. This is expected to generate a social control of attractiveness that ensures an honest expression of the sword according to body size, given that only the largest males would be able to express the longest swords without paying intra and intersexual costs. This reasoning is supported by the simulations presented in the third chapter where it is shown that the preference for attacking the most attractive competitors is a strategy that could invade the population and, once it is fixed, it could ensure a positive correlation between male quality and attractiveness. Thus, this mechanism, unlike the handicap principle, does not need to make assumptions about the biological details of the system. Therefore, when male quality is related to fighting ability, any potentially dishonest signal initially evolved to exploit female pre-existing biases could be controlled by such mechanism

Improving the welfare of a zoo-housed male drill (Mandrillus leucophaeus poensis) aggressive towards visitors

Improving captive animal welfare and maintaining its behavioral competence for future conservation purposes is of highest priority for zoos. The behavior of an aggressive male drill (Mandrillus leucophaeus poensis) was assessed in Barcelona zoo. The two-year study presented in this article examines the effects of introducing changes in the exhibit of the drill in order to improve its welfare by analyzing scan behaviors. First, a partial visual barrier was applied which proved to be insufficient to decrease the long-term stress indicators assessed. After this a feeding enrichment program was implemented. The results obtained supported our hypothesis that feeding and explorative activities would increase whereas apathetic and stereotypic behavior would decrease. However, the visitor-directed aggression did not vary, indicating that more profound structural modifications were needed to reduce the negative impact of the agonistic interactions between the drill and the public. The study emphasizes the usefulness of environmental enrichment evaluations in assessing captive animal welfare

Spatial learning based on visual landmarks in the freshwaterblenny Salaria fluviatilis (Asso, 1801)

The use and learning of visual landmarks seem to be strongly influenced by ecological demands and vary according to habitat, sex and, presumably, dominance status. In blennies, sexes differ in their home-range extension and this could predispose them to use different mechanisms to navigate. The main aim of this study was to investigate if Salaria fluviatilis (a benthonic and polyginic freshwater blenny) was able to solve a learning maze using direct visual landmarks. Performance between sexes was compared, and the possible relationship between the males' secondary sexual characteristics (SSCs) development and their spatial ability was considered. In this species, the SSCs consist of a cephalic crest and a pair of anal glands. Fish were subjected to 10 sessions (each one consisting of 11 consecutive trials) in a specially designed apparatus where they had to find the correct exit using direct visual landmarks. The proportion of males that learned the task (80%) was higher than that of females (30%). Cephalic crest development of the male was associated with a higher readiness to solve the spatial task. These results support the importance of ecological demands in shaping a species' spatial abilities. They also provide a comprehensive perspective that would link dominance (through cephalic crest development), learning and sexual selection

Parents' presence affects embryos' development in Salaria fluviatilis (Asso, 1801), a fish with parental care

In fishes, the parents' presence generally improves embryos' survival through parental care, but it is also associated with some disadvantages such as clutch cannibalism and loss of male physical condition. Captive breeding of the river blenny Salaria fluviatilis might improve if these disadvantages were avoided by artificially replacing parental care benefits in the lab. Before accepting this procedure, it should be studied whether embryo development is dependent or not on any other unknown effect related to the parents' presence. In this study, the ontogenetic sequence and several morphological structures - standard length, head height, jaw length and yolk-sac volume - from embryos reared both in the presence and in the absence of the parents were compared. At day 11 after oviposition, in the parents' absence treatment, well-developed embryos were obtained, but a smaller size of the yolk-sac, a greater head height and a tendency to have a greater jaw length than in the parents' presence treatment were found. These results suggest that the parents' presence might affect embryo development and perhaps offspring sexual determination. Given these differences, the practise of depriving clutches from their parents in captivity breeding programmes should be questioned

Boldness is related to the development of the cephalic crest in the male of the river blenny Salaria fluviatilis (Asso, 1801)

Boldness is defined as the tendency of an individual to take risks when exposed to novel objects or situations. The main aim of this work was to dilucidate if boldness was related to the development of the secondary sexual traits (SSTs) in the male of the river blenny Salaria fluviatilis, a freshwater fish which takes care of eggs. As a second objective SSTs effect on parental status adoption was also be explored. Wild young fish were caught in the Segre River (Ebro basin) in November 2010. Fish were kept in five aquaria in groups of eight males and eight females with artificial nests. Boldness (boldness score and hesitancy) of males (initially with little SSTs development) was tested as the time required to exit a refuge when exposed to a new environment. Fish were mantained in the same aquaria for several months, and males' SSTs development and reproductive behaviour were monitored. Boldness score was negatively associated to cephalic crest development. Hesitancy was negatively related to male length and was also influenced by the interaction between male length and cephalic crest. Parental status acquisition was positively related to the male's length, marginally related to anal gland development, and non-related to cephalic crest. These results suggest an intrasexual role of the crest as an informative trait of boldness (honest signal) which might not necessarily be chosen by the females. It is also discussed that correlational selection could be responsible for linking boldness and growth rate in this species. Sexual selection, in addition to having directed the evolution of secondary sexual traits, might have favored certain personality traits (e.g. boldness) associated with the achievement of a larger body length

Improving water quality does not guarantee fish health: Effects of ammonia pollution on the behaviour of wild-caught pre-exposed fish.

Ammonia is a pollutant frequently found in aquatic ecosystems. In fish, ammonia can cause physical damage, alter its behaviour, and even cause death. Exposure to ammonia also increases fish physiological stress, which can be measured through biomarkers. In this study, we analysed the effect of sublethal ammonia concentrations on the behaviour and the oxidative stress of Barbus meridionalis that had been pre-exposed to this compound in the wild. Wild-caught fish from a polluted site (pre-exposed fish) and from an unpolluted site (non-pre-exposed fish) were exposed, under experimental conditions, to total ammonia concentrations (TAN) of 0, 1, 5, and 8 mg/L. Swimming activity, feeding behaviour, and oxidative stress response based on biomarkers were analysed. Pre-exposed fish showed both an altered behaviour and an altered oxidative stress response in the control treatment (0 mg/L). Differences in swimming activity were also found as pre-exposed fish swam less. Lower feeding activity (voracity and satiety) and altered response to oxidative stress were also observed at 1 mg/L TAN. Biomarker results confirmed pre-exposed fish suffer from a reduction in their antioxidant defences and, hence, showed increased oxidative tissue damage. In summary, pre-exposed fish showed more sensitivity to ammonia exposure than fish from a pristine site

Improving the welfare of a zoo-housed male drill (Mandrillus 1 leucophaeus poensis) aggressive towards visitors 2

Improving captive animal welfare and maintaining its behavioral competence for future 17 conservation purposes is of highest priority for zoos. The behavior of an aggressive male 18 drill (Mandrillus leucophaeus poensis) was assessed in Barcelona zoo. The two-year study 19 presented in this article examines the effects of introducing changes in the exhibit of the 20 drill in order to improve its welfare by analyzing scan behaviors. First, a partial visual 21 barrier was applied which proved to be insufficient to decrease the long-term stress 22 indicators assessed. After this a feeding enrichment program was implemented. The results 23 obtained supported our hypothesis that feeding and explorative activities would increase 24 whereas apathetic and stereotypic behavior would decrease. However, the visitor-directed 25 aggression did not vary, indicating that more profound structural modifications were needed 26 to reduce the negative impact of the agonistic interactions between the drill and the public. 27 The study emphasizes the usefulness of environmental enrichment evaluations in assessing 28 captive animal welfare

Effects of industrial pollution on the reproductive biology of Squalius laietanus (Actinopterygii, Cyprinidae) in a Mediterranean stream (NE Iberian Peninsula)

Mediterranean rivers are severely affected by pollutants from industry, agriculture and urban activities. In this study, we examined how industrial pollutants, many of them known to act as endocrine disruptors (EDCs), could disturb the reproduction of the Catalan chub (Squalius laietanus). The survey was conducted throughout the reproductive period of S. laietanus (from March to July 2014) downstream an industrial WWTP located in the River Ripoll (NE Iberian Peninsula). Eighty fish (28 females and 52 males) were caught by electrofishing upstream and 77 fish (33 females and 44 males) downstream a WWTP. For both sexes, the gonadosomatic index (GSI) and gonadal histology were examined and related to water chemical analysis and fish biomarkers. Female fecundity was assessed using the gravimetric method. Fish from the polluted site showed enhanced biomarker responses involved in detoxification. Also, in the polluted site, lower GSI values were attained in both sexes and females displayed lower numbers of vitellogenic oocytes. Gonadal histology showed that allmaturation stages of testicles and ovaries were present at the two study sites but fish males from the polluted site had smaller diameter seminiferous tubules. Water chemical analysis confirmed greater presence of EDCs in the river downstream the industrial WWTP. The chemicals benzotriazole and benzothiazole could be partially responsible for the observed alterations in the reproductive biology of S. laietanus

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements