Biotic and abiotic forces govern the evolution of trophic niches, which profoundly impact ecological and evolutionary processes and aspects of species biology. Herbivory is a particularly interesting trophic niche because there are theorized trade-offs associated with diets comprised of low quality food that might prevent the evolution of herbivory in certain environments. Herbivory has also been identified as a potential evolutionary "dead-end" that hinders subsequent trophic diversification. For this study we investigated trophic niche evolution in Clupeoidei (anchovies, sardines, herrings, and their relatives) and tested the hypotheses that herbivory is negatively correlated with salinity and latitude using a novel, time-calibrated molecular phylogeny, trophic guilds delimited using diet data and cluster analysis, and standard and phylogenetically-informed statistical methods. We identified eight clupeoid trophic guilds: molluscivore, terrestrial invertivore, phytoplanktivore, macroalgivore, detritivore, piscivore, crustacivore, and zooplanktivore. Standard statistical methods found a significant negative correlation between latitude and the proportion of herbivorous clupeoids (herbivorous clupeoid species/total clupeoid species), but no significant difference in the proportion of herbivorous clupeoids between freshwater and marine environments. Phylogenetic least squares regression did not identify significant negative correlations between latitude and herbivory or salinity and herbivory. In clupeoids there were five evolutionary transitions from non-herbivore to herbivore guilds and no transitions from herbivore to non-herbivore guilds. There were no transitions to zooplanktivore, the most common guild, but it gave rise to all trophic guilds, except algivore, at least once. Transitions to herbivory comprised a significantly greater proportion of diet transitions in tropical and subtropical (<35°) relative to temperate areas (>35°). Our findings suggest cold temperatures may constrain the evolution of herbivory and that herbivory might act as an evolutionary "dead-end" that hinders subsequent trophic diversification, while zooplanktivory acts as an evolutionary "cradle" that facilitates trophic diversification.

The objective of this study was to determine the effect of temperature on growth and survival of larval and juvenile burbot, Lota lota maculosa. Burbot aquaculture is developing primarily in response to declining wild stocks and a need to restore such populations. Beyond conservation efforts, there is also potential to culture this species commercially. However, many important aspects of burbot culture remain unaddressed. In this study larval and juvenile burbot were reared at three constant water temperatures (10, 15, and 20°C) in an intensive culture setting. Two 30 day trials were conducted during the larval life stage and one 60 day trial during the juvenile life stage. In Trial 1, larval burbot (mean total length ± SD, 6.9 ± 1.0 mm, approximately 65 days post hatch) reared at 20°C grew the fastest, while growth was lowest in the 10°C treatment. Survival was inversely related to temperature, with the lowest average of 6.6% observed in larvae reared at 20°C. The percentage cannibalized was quantified and found to be positively correlated with water temperature, and reached 58.0% in larvae reared at 20°C. In Trial 2, as larvae approached metamorphosis (12.9 ± 1.9 mm, approximately 100 days post hatch), growth was also highest in fish at 20°C and lowest in those at 10°C. At this stage survival was higher in fish at lower temperatures, but the percentage cannibalized appeared independent of temperature, averaging over 50% in fish at all temperatures. In Trial 3, growth of juveniles (59.9 ± 12.4 mm, approximately 205 days post hatch) reared at 15 and 20°C was not significantly different, yet both displayed significantly increased growth relative to juveniles reared at 10°C. Juveniles were fully transitioned to a dry diet, and survival averaged > 93% in all culture temperatures. The percentage cannibalized during this life stage averaged b 5%, and was not affected by temperature. This study demonstrated the importance of water temperature, as it clearly affects culture performance of larval and juvenile burbot. Results from this study have implications for maximizing growth during larval and juvenile life stages of this species, and provide a comparative, empirical framework for establishing conservation, or commercial aquaculture programs for burbot.

Clupeiformes (herring, sardines, shad, anchovies and allies) are a globally distributed clade with nearly 400 marine, freshwater, and diadromous species. Although best known as filter feeding fishes that form large schools, this group occupies a diverse array of trophic guilds and habitats. Theory suggests that species richness in clades is modulated by ecological limits, which results in diversity-dependent clade growth, a pattern that most clades exhibit. As a trans-marine/freshwater clade that has undergone repeated transitions between marine and freshwaters, Clupeiformes are an excellent system for investigating the interplay between ecological diversity and macroevolutionary dynamics. In this study we review the systematics of Clupeiformes and explore discordance in phylogenetic relationships and divergence times between mitochondrial and nuclear loci. We then use comparative methods to test whether ecological limits regulate diversity in Clupeiformes. We find discordance in phylogenetic relationships at various taxonomic scales, but also considerable agreement between genomes. Our results suggest that trans-marine/freshwater clades are able to circumvent ecological limits on clade growth at regional, but not on local scales. Our study demonstrates that phylogenies are a critical link between ecology and macroevolutionary dynamics, and suggests habitat transitions can play a key role in shaping diversity patterns, particularly in the neotropics.