| Jaw mechanics and dietary breadth in the sister atherinopsids California grunion Leuresthes tenuis and Gulf grunion L. sardina were compared to three other members of the clade Atherinopsini to test whether the two grunion species have evolved a novel jaw protrusion that might be associated with a narrow diet consisting of abundant prey. Quantitative comparison of cleared-and-stained specimens of the five species showed that, compared to false grunion Colpichthys regis, topsmelt Atherinops affinis, and jacksmelt Atherinopsis californiensis , L. tenuis and L. sardina have longer, more downwardly directed premaxillary protrusion, expanded dentary and premaxillary bones, greater lower jaw rotation, and larger premaxillary-vomer spacing. L. tenuis showed the most divergence in these features. For dietary analysis, adult L. tenuis and A. affinis were collected offshore, simultaneously with zooplankton samples to represent prey availability. L. tenuis fed heavily on mysid crustaceans, and, as predicted, had a narrower diet than A. affinis in the same habitat, as shown by higher L selectivity and lower H' diversity and J evenness values. Information available on As. californiensis and C. regis indicates that these species have broad diets associated with benthic feeding. High-speed video analysis shows that L. tenuis protrudes its jaws faster than A. affinis. The grunion sisters, especially L. tenuis, appear to have evolved a unique jaw mechanism that may allow efficient feeding on common, evasive prey. |
