Selecció sexual: per què els mascles lluiten i les femelles trien?

The struggle to reproduce is a key part of the existence of any organism. For sexually reproductive species, reproduction is more difficult because they need to find another individual willing to mate. Charles Darwin was the first to study mating systems from an evolutionary point of view and he laid the first stone of sexual selection theory. More than one century was needed to convince the scientific community of its validity, but it has become one of the most active areas in the field of evolutionary biology. According to the theory, the traits that give individuals higher reproductive output, though they often compromise their survival, may be selected by two different mechanisms. First, individuals of the same sex compete with each other to copulate with the other sex, so any character that makes them good competitors should be selected. Second, the individuals of a given sex, usually the females, are able to choose which individual they prefer to mate with, so they can select attractive traits in the eyes of the other sex. From this perspective, sexual selection theory has explained why males usually fight and females are the choosy sex. In addition, it has increased understanding of a great variety of extravagant behaviours in the context of sex: furtive mating, cross-dressing lovers, nuptial gifts and sexual suicide. Everything counts in the struggle for reproduction!La lluita per aconseguir reproduir-se és una part essencial de l’existència de qualsevol organisme. Per als animals sexuats, l’afer es veu complicat per la necessitat de trobar un altre individu disposat a aparellar-se. Charles Darwin va ser el primer que va estudiar els sistemes d’aparellament des d’una òptica evolutiva i va posar la primera pedra de la teoria de la selecció sexual. Tot i que va caldre més d’un segle per convèncer els científics de la seva validesa, ha esdevingut una de les àrees més fecundes en el camp de la biologia evolutiva. Segons la teoria, els caràcters que confereixen als individus més possibilitats de deixar descendència, malgrat que puguin comprometre la seva supervivència, seran seleccionats per dos mecanismes diferents. Per una banda, els individus d’un mateix sexe competiran entre si per aconseguir aparellar-se amb l’altre sexe, de manera que se seleccionaran caràcters que els facin bons competidors. Per altra banda, els individus d’un sexe, generalment les femelles, podran elegir quin individu els fa més el pes per aparellar-s’hi, de manera que es podran seleccionar trets que per alguna raó fan els individus més atractius a ulls de l’altre sexe. Sota aquesta perspectiva, la teoria de la selecció sexual ha mirat d’explicar perquè són els mascles els que normalment lluiten i perquè les femelles les que majoritàriament són més exigents a l’hora d’escollir parella. A més, ha permès entendre una gran varietat de comportaments extravagants en el context del sexe: còpules furtives, amants transvestits, regals nupcials o suïcidis sexuals. Tot s’hi val en la lluita per la reproducció

Relative brain size and its relation with the associative pallium in birds

Despite growing interest in the evolution of enlarged brains, the biological significance of brain size variation remains controversial. Much of the controversy is over the extent to which brain structures have evolved independently of each other (mosaic evolution) or in a coordinated way (concerted evolution). If larger brains have evolved by the increase of different brain regions in different species, it follows that comparisons of the whole brain might be biologically meaningless. Such an argument has been used to criticize comparative attempts to explain the existing variation in whole-brain size among species. Here, we show that pallium areas associated with domain-general cognition represent a large fraction of the entire brain, are disproportionally larger in large-brained birds and accurately predict variation in the whole brain when allometric effects are appropriately accounted for. While this does not question the importance of mosaic evolution, it suggests that examining specialized, small areas of the brain is not very helpful for understanding why some birds have evolved such large brains. Instead, the size of the whole brain reflects consistent variation in associative pallium areas and hence is functionally meaningful for comparative analyses

Relative brain size is associated with natal dispersal rate and species' vulnerability to climate change in seabirds

The cognitive buffer hypothesis proposes that species with larger brains (relative to their body size) exhibit greater behavioural flexibility, conferring an advantage in unpredictable or novel environments. Therefore, behavioural flexibility – and relative brain size – are likely to be important predictors of a species' vulnerability to anthropogenic pressures and, ultimately, extinction risk. However, current evidence linking brain size to species' vulnerability and extinction risk is inconclusive. Furthermore, studies examining the relationship between relative brain size and behavioural flexibility have mainly focused on foraging innovations, whilst other forms of behavioural flexibility remain unexplored. In this study, we collate species-specific information and examine links between relative brain size, rates of natal and adult dispersal (a measure of flexibility in breeding site fidelity), vulnerability to six anthropogenic threats and extinction risk for 131 species of seabird. We focused our study on seabirds, a highly threatened group that displays large variation in both relative brain size and dispersal behaviour. We found a significant positive relationship between relative brain size and natal dispersal rate, suggesting that relative brain size could enhance flexibility in breeding site choice in seabirds, consistent with the cognitive buffer hypothesis. However, this relationship does not persist when we consider adult dispersal, possibly reflecting constraints imposed by mate selection and knowledge transfer in seabirds. We also show that relative brain size is negatively associated with vulnerability to climate change. These findings have immediate application for predicting interspecific variation in species' vulnerability to climate change and identifying priority species for conservation

Coexistence of predators in time : Effects of season and prey availability on species activity within a Mediterranean carnivore guild

The degree of coexistence among predators can determine the structure of ecological communities. Niche partitioning is a common strategy applied by species to enhance their coexistence. Diet, habitat, or time use can be responsible for segregation among carnivore species, the latter factor being the least studied in Mediterranean ecosystems. Terrestrial medium-sized carnivores (i.e., mesocarnivores) carry out important functions in ecosystems, and identifying their interactions is essential for their conservation. In this study, we explore the activity of a terrestrial mesocarnivore guild in order to determine seasonal differences in daily activity patterns of competitors and prey. We also investigate how the abundance of a common mesocarnivore prey in the region, small mammals, influences the activity of predators. During a year, camera trap devices (n = 18) were installed in Montseny Natural Park (Catalan Pre-Coastal Range, North-East Iberian Peninsula), a region that hosts five mesocarnivore species. Camera trapping detections were used to estimate their daily activity patterns and corresponding overlaps. We also surveyed small mammal plots (n = 5) in order to calculate prey abundance and test its effect on the relative activity of each carnivore species. Despite all target mesocarnivores are mainly nocturnal, the activity overlap among them varies according to species particularities and season. Red fox (Vulpes vulpes) appears as a generalist species in terms of time use, whereas stone marten (Martes foina) and genet (Genetta genetta) show the most similar activity patterns and both of them seem to be positively influenced by small mammal abundance. Overall, the diversity found in the way mesocarnivore species use time could facilitate their coexistence. Despite activity pattern similarities among carnivore species should not be directly translated to negative interactions, they can have a strong influence in habitat and resource-limited ecosystems. Therefore, activity overlaps should be taken into account when discussing wildlife management actions

Brain size and evolutionary diversification in birds

The role of behavior in evolution remains controversial, despite that some ideas are over 100 years old. Changes in behavior are generally believed to enhance evolution by exposing individuals to new selective pressures and by facilitating range expansions. However, this hypothesis lacks firm empirical evidence. Moreover, behavioral changes can also inhibit evolution by hiding heritable variation from natural selection. Taking advantage of the complete phylogeny of extant birds, a new species-level measure of past diversification rate and the best existing measures of brain size (n = 1326 species), I show here that relative brain size is associated (albeit weakly) with diversification rates. Assuming that brain relative size reflects behavioral flexibility, an assumption well-supported by evidence, this finding supports the idea that behavior can enhance evolutionary diversification. This view is further supported by the discovery that the most important factor influencing diversification rates is ecological generalism, which is believed to require behavioral flexibility. Thus, behavioral changes that expose animals to a variety of environments can have played an important role in the evolution of birds

Niche filling predicts evolutionary trajectories in insular bird communities

•1. Different theories have been proposed to explain the phenotypic changes observed in island lineages, but it remains unclear if predictable evolutionary trajectories can be identified within island communities. •2. Using a 3D functional space approach, we tested whether insular endemic species tend to evolve towards apparent holes in niche space (expecting niche filling) or tend to become generalists, that is, moving towards the centre of the functional space (expecting niche expansion). •3. We tested these two hypotheses in 378 insular endemic species from 24 islands of 8 archipelagos, including 177 prehistoric anthropogenically extinct species. Analyses were conducted with and without accounting for species size difference. •4. We found that 57% of island endemic species evolved towards more unoccupied regions of the global morphospace (i.e. more distinct body sizes compared to the ones of their ancestors), suggesting a tendency for niche filling. When adjusted traits for body size, we found that half of the endemic species (50%) showed more distinct trait values than their ancestors. •5. Results also revealed that certain dietary niches (terrestrial herbivores and nectarivores) evolved distinct body sizes more frequently. Differences noted between islands and archipelagos suggest that biogeographic factors may influence evolutionary trajectory and interactions between these two hypotheses. •6. Our study confirms that extinct species occupied specific niches that have been left vacant, suggesting that these evolutionary ‘oddities’ could be more sensitive to extinction. Overall, it calls for a global assessment of the avian functional diversity lost from recent extinctions

Undiscovered bird extinctions obscure the true magnitude of human-driven extinction waves

Birds are among the best-studied animal groups, but their prehistoric diversity is poorly known due to low fossilization potential. Hence, while many human-driven bird extinctions (i.e., extinctions caused directly by human activities such as hunting, as well as indirectly through human-associated impacts such as land use change, fire, and the introduction of invasive species) have been recorded, the true number is likely much larger. Here, by combining recorded extinctions with model estimates based on the completeness of the fossil record, we suggest that at least ~1300–1500 bird species (~12% of the total) have gone extinct since the Late Pleistocene, with 55% of these extinctions undiscovered (not yet discovered or left no trace). We estimate that the Pacific accounts for 61% of total bird extinctions. Bird extinction rate varied through time with an intense episode ~1300 CE, which likely represents the largest human-driven vertebrate extinction wave ever, and a rate 80 (60–95) times the background extinction rate. Thus, humans have already driven more than one in nine bird species to extinction, with likely severe, and potentially irreversible, ecological and evolutionary consequences

Efecte de les variables ambientals i hidrològiques sobre la riquesa i distribució dels briòfits fontinals a la Catalunya oriental

Els briòfits tenen uns trets funcionals que fan d'ells uns dels indicadors més sensibles als canvis ambientals. En aquest treball vam estudiar si la riquesa d'espècies de briòfits i llurs distribucions es podien predir fent servir variables macroecològiques (p. ex., el clima, l'altitud i la conductivitat i el pH de l'aigua) a partir del mostreig de les comunitats de briòfits de 198 fonts distribuïdes entre la Serralada Litoral Central, el massissos del Montseny-Guilleries, el Lluçanès i la Garrotxa. Fent servir regressions lineals, vam relacionar les variables ambientals amb la riquesa d'espècies per font. Seguidament, mitjançant un anàlisi de components principals (ACP), vam agrupar les variables ambientals en tres eixos descriptius de la variabilitat ambiental de les fonts. Fent servir les variables ambientals i els tres eixos extrets de la ACP, vam comprovar la influència d'aquestes sobre la distribució d'espècies fent servir anàlisis de la variància (ANOVA). Els nostres resultats suggereixen que la riquesa d'espècies està positivament relacionada amb la precipitació anual, el pH de l'aigua de la font i l'altitud a la que es troba la surgència. Tanmateix, la variància explicada pel model va ser força baixa (Bryophytes have biological traits that make them some of the most sensitive indicators of environmental change. Springs have a significant presence of bryophytes and hence they are ideal habitats for studying their relationship with the environment. We tested whether bryophyte species richness and distribution can be predicted with macroecological variables (i.e., climate, altitude, water pH and conductivity) sampling bryophytes from 198 springs distributed along montane regions in NE Iberian Peninsula. Regressions were used to relate species richness with selected environmental variables. A PCA analysis was performed to reduce the environmental variables to three principal coordinates. We tested the influence of environmental variables and PCA axis on species distribution using ANOVAs. Our results suggest that species richness is related to mean annual precipitation, water pH and altitude. However, total variance explained by the model is low

Environmental variation and the evolution of large brains in birds

Environmental variability has long been postulated as a major selective force in the evolution of large brains. However, assembling evidence for this hypothesis has proved difficult. Here, by combining brain size information for over 1,200 bird species with remote-sensing analyses a to estimate temporal variation in ecosystem productivity, we show that larger brains (relative to body size) are more likely to occur in species exposed to larger environmental variation throughout their geographic range. Our reconstructions of evolutionary trajectories are consistent with the hypothesis that larger brains (relative to body size) evolved when the species invaded more seasonal Regions. However, the alternative-that the species already possessed larger brains when they invaded more seasonal regions-cannot be completely ruled out. Regardless of the exact mechanism, our findings provide strong empirical support for the association between large brains and environmental variability

Neuron numbers link innovativeness with both absolute and relative brain size

A longstanding issue in biology is whether the intelligence of animals can be predicted by absolute or relative brain size. However, progress has been hampered by an insufficient understanding of how neuron numbers shape internal brain organization and cognitive performance. On the basis of estimations of neuron numbers for 111 bird species, we show here that the number of neurons in the pallial telencephalon is positively associated with a major expression of intelligence: innovation propensity. The number of pallial neurons, in turn, is greater in brains that are larger in both absolute and relative terms and positively covaries with longer post-hatching development periods. Thus, our analyses show that neuron numbers link cognitive performance to both absolute and relative brain size through developmental adjustments. These findings help unify neuro-anatomical measures at multiple levels, reconciling contradictory views over the biological significance of brain expansion. The results also highlight the value of a life history perspective to advance our understanding of the evolutionary bases of the connections between brain and cognition