Scale and tempo of brain expansion in the course of human evolution implies that this process was driven by a positive feedback. The ‘cultural drive’ hypothesis suggests a possible mechanism for the runaway brain-culture coevolution wherein high-fidelity social learning results in accumulation of cultural traditions which, in turn, promote selection for still more efficient social learning. Here we explore this evolutionary mechanism by means of computer modeling. Simulations confirm its plausibility in a social species in a socio-ecological situation that makes the sporadic invention of new beneficial and cognitively demanding behaviours possible. The chances for the runaway brain-culture coevolution increase when some of the culturally transmitted behaviours are individually beneficial while the others are group-beneficial. In this case, ‘cultural drive’ is possible under varying levels of between-group competition and migration. Modeling implies that brain expansion can receive additional boost if the evolving mechanisms of social learning are costly in terms of brain expansion (e.g., rely on complex neuronal curcuits) and tolerant to the complexity of information transferred, that is, make it possible to transfer complex skills and concepts easily. Human language presumably fits this description. Modeling also confirms that the runaway brain-culture coevolution can be accelerated by additional positive feedback loops via population growth and lifespan extension, and that between-group competition and cultural group selection can facilitate the propagation of group-beneficial behaviours and remove maladaptive cultural traditions from the population’s culture, which individual selection is unable to do.
The stock-specific distribution of maturing and adult salmon in the Northeast (NE) Pacific has been a persistent information gap that has prevented us from determining the ocean conditions experienced by individual stocks. This continues to impede understanding of the role of ocean conditions in stock-specific population dynamics. We assessed scale archives for 17 sockeye salmon (Oncorhynchus nerka) stocks covering the entire North Pacific, from the Columbia River to Kamchatka Peninsula, to define salmon locations during their last growing season before returning to their spawning grounds. We used the relationship between δ13C in salmon scales and sea water temperature to estimate salmon distribution based on correlation strength. Significant correlations were found for 13 of the stocks allowing us to define feeding grounds with confidence. Complementary information from δ15N, historical tagging studies, and connectivity analysis were used to further refine distribution estimates. Based on the estimated distributions of the NE Pacific stocks, we suggest a sequence of steps that could result in salmon marine distributions. This study is a first step toward determining stock-specific distributions of salmon in the NE Pacific, and provides a basis for the application of the approach to other salmon scale archives. This information will improve our ability to relate stock dynamics to ocean conditions, ultimately enabling improved stock management. For example, our estimated distributions of Bristol Bay and NE Pacific stocks demonstrated that they occupy different areas with a number of the former being distributed in the high productivity shelf waters of the Aleutian Islands and Bering Sea. This may explain while these stocks seem to have responded differently to changes in ocean conditions, and the long term trend of increased productivity of Bristol Bay sockeye.
The European eel (Anguilla anguilla) is critically endangered throughout its distribution range. Knowledge about age distribution of future spawners (silver eels) is essential to monitor the status and contribute to the recovery of this species. Determination of age in anguillid eels is challenging, especially in eels from the northern part of the distribution area where growth is slow and age at maturation can be up to 30 years or more. Eels from the river Imsa in Norway have been monitored since 1975 and this reference time-series has been used to assess the stock at the European level. Population dynamics in this catchment were analyzed during the late 1980s by estimating ages on whole cleared otoliths. However, techniques for revealing annual increments on otoliths have evolved over the years sometimes yielding significant differences in age estimates. In this study, the historical otolith data were reanalyzed using a grinding and polishing method rather than reading the whole otolith. The new age estimates were considerably higher than the previous ones, sometimes by up to 29 years. Since the 1980s, mean age of silver eels only slightly increased (from 19 to 21 years in the 2010s). This was mainly due to the disappearance of younger silver eels (less than 15 years) in the 2010s. The new age estimates agreed with the steep decline in recruitment which occurred in the late 1980s in the Imsa catchment. Growth (30 mm y-1) has not changed since the 1980s, although density in the catchment has decreased. Revealing and reading age of slow growing eels remain a challenge but adding a measure of otolith reading uncertainty may improve age data collection and contribute to recovery measures for this species.
Sickness behaviour is a taxonomically-widespread coordinated set of behavioural changes that in- creases shelter-seeking while reducing levels of general activity, as well as food (anorexia) and water (adipsia) consumption, when fighting infection by pathogens and disease. The leading hypothesis ex- plaining such sickness-related shifts in behaviour is the energy conservation hypothesis. This hypothe- sis argues that sick (i.e. immune-challenged) animals reduce energetic expenditure in order have more energy to fuel an immune response, which in some vertebrates, also includes producing an energetically- expensive physiological fever. We experimentally tested the hypothesis that an immune-challenge with lipopolysaccharide (LPS) will cause Gryllus firmus field crickets to reduce their activity, increase shelter- use and avoid foods that interfere with an immune response (i.e. fat) while preferring a diet thats fuel an immune response (i.e. protein). We found little evidence of sickness behaviour in Gryllus firmus as immune-challenged individuals did not reduce their activity or increase their shelter-seeking. Neither did we observe changes in feeding or drinking behaviour nor a preference for protein or avoidance of lipids. Males tended to use shelters less than females but no other behaviours differed between the sexes. The lack of sickness behaviour in our study might reflect the fact that invertebrates do not possess energetically-expensive physiological fever as part of their immune response. Therefore, there is little reason to conserve energy via reduced activity or increased shelter use when immune-challenged.
Reproductive character displacement is a pattern whereby sympatric lineages diverge more in reproductive character morphology than allopatric lineages. This pattern has been observed in many plant species, but comparably few have sought to disentangle underlying mechanisms. Here, in a hyperdiverse lineage of Neotropical plants (Ruellia; Acanthaceae), we present evidence of reproductive character displacement in a macroevolutionary framework (i.e., among species) and document mechanistic underpinnings. In a series of inter-specific hand pollinations in a controlled glasshouse environment, we found that crosses between species that differed more in overall flower size, particularly in style length, were significantly less likely to produce viable seeds. Further, species pairs that failed to set seed were more likely to have sympatric distributions in nature. While these findings could result from competition for pollinators or differential fusion of sympatric populations based on variable crossability, our results instead lend support for a role of reinforcement whereby selection has acted to increase reproductive barriers between sympatric species, especially given divergence in floral traits less likely to be under selection by pollinators (i.e., style length). Our results add to growing evidence that character displacement contributes to exceptional floral diversity of angiosperms.