Potential enhanced ability of giant squid to detect sperm whales is an exaptation tied to their large body size

It has been hypothesized that sperm whale predation is the driver of eye size evolution in giant squid. Given that the eyes of giant squid have the size expected for a squid this big, it is likely that any enhanced ability of giant squid to detect whales is an exaptation tied to their body size. Future studies should target the mechanism behind the evolution of large body size, not eye size. Reconstructions of the evolutionary history of selective regime, eye size, optical performance, and body size will improve the understanding of the evolution of large eyes in large ocean animals

The Cost of Bearing a Sword: Locomotor Costs and Compensations in Relation to a Sexually Selected Trait in Xiphophorus

Some of the most compelling traits to evolutionary biologists are sexually selected traits. The `un-natural' expression of these traits has puzzled biologists since the time of Charles Darwin. Why would a trait evolve that seems to decrease survival? Most of these traits evolve because they increase the reproductive fitness of the bearer, either through intra-sexual or inter-sexual competition. However, these sexually selected traits must meet the demands of both natural and sexual selection. It is therefore assumed that there are `costs' associated with the trait that limits their expression. In this dissertation I examined the performance costs of a sexually selected trait, expressed as an exaggerated morphological structure. I first introduce a more integrative approach to the study of detecting costs of sexually selected traits. This approach incorporates additional aspects of the organism's phenotype that may have evolved to offset the costs of the sexually selected trait. I show that ignoring these `compensatory' traits may mask the cost of the sexually selected trait using synthesized data. I then set out to examine the repeatability of various swimming performance measures. Using male guppies (Poecilia reticulata) I demonstrate that swimming performance measures are stable over various time scales. Both aerobic and anaerobic locomotor functions were examined over time scales varying from days to more than a year later. While most performance measures were not stable over a year, at least one was repeatable. Furthermore, although most performance measures decreased over a year, one significantly increased (maximum speed, Umax). I then used phylogenetic comparative methods to determine the locomotor costs of the sexually selected `sword' among species of Xiphophorus and Priapella, taking into account compensatory traits. I showed that inter-specifically, the sword is not a cost to critical swimming speed among 19 species of Xiphophorus and Priapella. In fact, when compensatory traits and phylogenetic information are included, the sword had a significant positive effect on critical swimming speed among these species. This suggests that as this sexually selected trait evolved it was not a locomotor handicap

Data from: Convergent evolution of locomotor morphology but not performance in gymnotiform swimmers

Convergent evolution of a novel locomotor strategy implies that a fitness benefit may be associated with the new gait. Opportunities to study this phenomenon are often constrained by a lack of transitional taxa, but teleost fishes offer examples of extant species across such evolutionary shifts in gait. For instance, one species from Osteoglossiformes and the entire order of Gymnotiformes independently evolved a novel gait, gymnotiform locomotion, where thrust is produced by the undulation of an elongate anal fin. Here, we investigate whether this convergence in gait is also associated with similarities in shape, burst swimming abilities, and/or steady‐swimming energetics. Specifically, we measured body and fin morphology of fish within Gymnotiformes and Osteoglossiformes, along with closely related Siluriformes and Cypriniformes, to examine the link between gymnotiform locomotion and morphology in a phylogenetic context. Second, we tested the burst swimming capabilities and oxygen consumption during endurance swimming of a subset of the same gymnotiform, osteoglossiform, and cypriniform species, including “transitional” Osteoglossiformes that exhibit intermediate gaits, to determine if the evolution of this specialized gait is associated with a change in either of these performance metrics. Our results suggest that convergence on the gymnotiform gait is associated with morphological convergence, but does not constrain a fish's maximum sprinting speeds or their energetic demands during steady swimming

Climate Data wo Costa Rican Species

Mean trait values, standard errors, and climate date for each of our source populations and study specie

Data from: Iterative evolution of increased behavioral variation characterizes the transition to sociality in spiders and proves advantageous

The evolution of group living is regarded as a major evolutionary transition and is commonly met with correlated shifts in ancillary characters. We tested for associations between social tendency and a myriad of abiotic variables and behavioral traits (e.g., boldness, activity level) in a clade of spiders that exhibit highly variable social structures.We found that social species tended to exhibit reduced aggressiveness towards prey, increased fearfulness towards predators, reduced activity levels, and occurred in warm, wet habitats with low wind velocities. Within-species variation in aggressiveness and boldness were greater in social species. We then assessed the functional consequences of within-species trait variation on reconstituted colonies of four species (A. eximius, A. rupununi, A. guacamayos, A. oritoyacu). We used colonies consisting of known ratios of docile versus aggressive individuals and group foraging success as a measure of colony performance.We found that groups composed of a mixture of docile and aggressive individuals outperformed monotypic groups: (1) mixed groups were more effective at subduing medium and large sized prey, and (2) mixed groups collectively gained more mass during shared feeding events. Our results suggest that the iterative evolution of depressed aggressiveness and increased within-species behavioral variation in social spiders is advantageous, and could be an adaptation to group living that is analogous to the formation of morphological castes within the social insect

Latitudinal and Climatic Variation in Body Size and Dorsal Scale Counts in Sceloporus Lizards: A Phylogenetic Perspective

Squamates often follow an inverse Bergmann\u27s rule, with larger-bodied animals occurring in warmer areas or at lower latitudes. The size of dorsal scales in lizards has also been proposed to vary along climatic gradients, with species in warmer areas exhibiting larger scales, putatively to reduce heat load. We tested for these patterns in the diverse and widespread lizard genus Sceloporus. Among 106 species or populations, body size was associated positively with maximum temperature (consistent with the inverse of Bergmann\u27s rule) and aridity, but did not covary with latitude. Scale size (inferred from the inverse relation with numbers of scales) was positively related to body size. Controlling for body size via multiple regression, scale size was associated negatively with latitude (best predictor), positively with minimum temperature, and negatively with aridity (similar results were obtained using scores from a principal components analysis of latitude and climatic indicators). Thus, lizards with larger scales are not necessarily found in areas with higher temperatures. Univariate analyses indicated phylogenetic signal for body size, scale counts, latitude, and all climate indicators. In all cases, phylogenetic regression models fit the data significantly better than nonphylogenetic models; thus, residuals for log10 number of dorsal scale rows exhibited phylogenetic signal

Intermediate Kinematics Produce Inferior Feeding Performance in a Classic Case of Natural Hybridization

Selection on naturally occurring hybrid individuals is a key component of speciation theory, but few studies examine the functional basis of hybrid performance. We examine the functional consequences of hybridization in nature, using the freshwater sunfishes (Centrarchidae), where natural hybrids have been studied for more than a century and a half. We examined bluegill (Lepomis macrochirus), green sunfish (Lepomis cyanellus), and their naturally occurring hybrid, using prey-capture kinematics and morphology to parameterize suction-feeding simulations on divergent parental resources. Hybrid individuals exhibited kinematics intermediate between those of the two parental species. However, performance assays indicated that hybrids display performance most similar to the worse-performing species for a given parental resource. Our results show that intermediate hybrid phenotypes can be impaired by a less-than-intermediate performance and hence suffer a larger loss in fitness than could be inferred from morphology alone

Data from: Intermediate kinematics produce inferior feeding performance in a classic case of natural hybridization

Selection on naturally-occurring hybrid individuals is a key component of speciation theory, but few studies examine the functional basis of hybrid performance. We examine the functional consequences of hybridization in nature using the freshwater sunfishes (Centrarchidae), where natural hybrids have been studied for over a century and a half. We examined bluegill (Lepomis macrochirus), green sunfish (Lepomis cyanellus), and their naturally-occurring hybrid using prey capture kinematics and morphology to parameterize suction feeding simulations on divergent parental resources. Hybrid individuals exhibited intermediate kinematics between the two parental species. However, performance assays indicated that hybrids display performance most similar to the worse-performing species for a given parental resource. Our results show that intermediate hybrid phenotypes can be impaired by a less than intermediate performance and hence suffer a larger loss in fitness than could be inferred from morphology alone