Gametic isolation is thought to play an important role in the evolution of reproductive isolation in broadcast-spawning marine invertebrates. However, it remains uncertain whether gametic isolation typically develops early in the speciation process or accumulates after other reproductive barriers are already in place. It is also unknown whether gametic incompatibilities have effectively prevented introgression during later stages of divergence. Here, we use phylogenomic approaches to test whether the well-documented asymmetric gametic incompatibilities between strongylocentrotid urchins have been effective in preventing introgression. Despite a well-supported species tree, we found considerable phylogenetic discordance that cannot be explained by incomplete lineage sorting alone. There was strong support for introgression between at least four pairs of extant taxa: S. pallidus ↔ S. droebachiensis, S. intermedius ↔ S. pallidus, S. purpuratus ↔ S. fragilis, and M. franciscanus ↔ P. depressus. There was additional evidence for introgression on internal branches of the phylogeny. Although gametic incompatibilities may be important in species recognition and the maintenance of species boundaries in strongylocentrotid urchins, gametic isolation does not appear to have been an effective barrier to introgression. The continued divergence in the face of widespread introgression indicates that other reproductive isolating barriers likely exist and may have been more critical in establishing reproductive isolation early in speciation.

Shallow lakes and ponds constitute a significant number of water bodies worldwide. Many are heterotrophic, indicating that they are likely net contributors to global carbon cycling. Climate change is likely to have important impacts on these waterbodies. In this study, we examined two small Minnesota ponds; a permanent woodland pond and a temporary prairie pond. The woodland pond had lower levels of phosphorus and phytoplankton than the prairie pond. Using the open water oxygen method, we found the prairie pond typically had a higher level of gross primary production (GPP) and respiration (R) than the woodland pond, although the differences between the ponds varied with season. Despite the differences in GPP and R between the ponds the net ecosystem production was similar with both being heterotrophic. Since abundant small ponds may play an important role in carbon cycling and are likely to undergo changes in temperature and hydroperiod associated with climate change, understanding pond metabolism is critical in predicting impacts and designing management schemes to mitigate changes.

Gametic isolation is thought to play an important role in the evolution of reproductive isolation in broadcast-spawning marine invertebrates. However, it remains uncertain whether gametic isolation typically develops early in the speciation process or accumulates after other reproductive barriers are already in place. It is also unknown whether gametic incompatibilities have effectively prevented introgression during later stages of divergence. Here, we use phylogenomic approaches to test whether the well-documented asymmetric gametic incompatibilities between strongylocentrotid urchins have been effective in preventing introgression. Despite a well-supported species tree, we found considerable phylogenetic discordance that cannot be explained by incomplete lineage sorting alone. There was strong support for introgression between at least four pairs of extant taxa: S. pallidus ↔ S. droebachiensis, S. intermedius ↔ S. pallidus, S. purpuratus ↔ S. fragilis, and M. franciscanus ↔ P. depressus. There was additional evidence for introgression on internal branches of the phylogeny. Although gametic incompatibilities may be important in species recognition and the maintenance of species boundaries in strongylocentrotid urchins, gametic isolation does not appear to have been an effective barrier to introgression. The continued divergence in the face of widespread introgression indicates that other reproductive isolating barriers likely exist and may have been more critical in establishing reproductive isolation early in speciation.

Gametic isolation is thought to play an important role in the evolution of reproductive isolation in broadcast-spawning marine invertebrates. However, it remains uncertain whether gametic isolation typically develops early in the speciation process or accumulates after other reproductive barriers are already in place. It is also unknown whether gametic incompatibilities have effectively prevented introgression during later stages of divergence. Here, we use phylogenomic approaches to test whether the well-documented asymmetric gametic incompatibilities between strongylocentrotid urchins have been effective in preventing introgression. Despite a well-supported species tree, we found considerable phylogenetic discordance that cannot be explained by incomplete lineage sorting alone. There was strong support for introgression between at least four pairs of extant taxa: S. pallidus ↔ S. droebachiensis, S. intermedius ↔ S. pallidus, S. purpuratus ↔ S. fragilis, and M. franciscanus ↔ P. depressus. There was additional evidence for introgression on internal branches of the phylogeny. Although gametic incompatibilities may be important in species recognition and the maintenance of species boundaries in strongylocentrotid urchins, gametic isolation does not appear to have been an effective barrier to introgression. The continued divergence in the face of widespread introgression indicates that other reproductive isolating barriers likely exist and may have been more critical in establishing reproductive isolation early in speciation.