Unpalatability of viceroy butterflies (Limenitis archippus) and their purported mimicry models,Florida queens (Danaus gilippus)

Summary Understanding the dynamics of defensive mimicry requires accurately characterizing the comparative palatability of putative models and mimics. The Florida viceroy butterfly (Limenitis archippus floridensis) is traditionally considered a palatable Batesian mimic of the purportedly distasteful Florida queen (Danaus gilippus berenice). I re-evaluated this established hypothesis by directly assessing palatability of viceroys and queens to red-winged blackbirds in a laboratory experiment. Representative Florida viceroys were surprisingly unpalatable to red-wings; only 40% of viceroy abdomens were entirely eaten (compared to 98% of control butterfly abdomens), and nearly one-third were immediately tasterejected after a single peck. In fact, the viceroys were significantly more unpalatable than representative Florida queens, of which 65% were eaten and 14% taste-rejected. Thus, viceroys and queens from the sampled populations exemplify Müllerian rather than Batesian mimicry, and the viceroy appears to be the stronger model. These findings prompt a reassessment of the ecological and evolutionary dynamics of this classic mimicry relationship.     

Evolutionary stasis in Euphorbiaceae pollen: selection and constraints

Although much attention has been paid to the role of stabilizing selection, empirical analyses testing the role of developmental constraints in evolutionary stasis remain rare, particularly for plants. This topic is studied here with a focus on the evolution of a pollen ontogenetic feature, the last points of callose deposition (LPCD) pattern, involved in the determination of an adaptive morphological pollen character (aperture pattern). The LPCD pattern exhibits a low level of evolution in eudicots, as compared to the evolution observed in monocots. Stasis in this pattern might be explained by developmental constraints expressed during male meiosis (microsporogenesis) or by selective pressures expressed through the adaptive role of the aperture pattern. Here, we demonstrate that the LPCD pattern is conserved in Euphorbiaceae s.s. and that this conservatism is primarily due to selective pressures. A phylogenetic association was found between the putative removal of selective pressures on pollen morphology after the origin of inaperturate pollen, and the appearance of variation in microsporogenesis and in the resulting LPCD pattern, suggesting that stasis was due to these selective pressures. However, even in a neutral context, variation in microsporogenesis was biased. This should therefore favour the appearance of some developmental and morphological phenotypes rather than others.     

Did the notochord evolve from an ancient axial muscle? The axochord hypothesis

The origin of the notochord is one of the key remaining mysteries of our evolutionary ancestry. Here, we present a multi‐level comparison of the chordate notochord to the axochord, a paired axial muscle spanning the ventral midline of annelid worms and other invertebrates. At the cellular level, comparative molecular profiling in the marine annelids P. dumerilii and C. teleta reveals expression of similar, specific gene sets in presumptive axochordal and notochordal cells. These cells also occupy corresponding positions in a conserved anatomical topology and undergo similar morphogenetic movements. At the organ level, a detailed comparison of bilaterian musculatures reveals that most phyla form axochord‐like muscles, suggesting that such a muscle was already present in urbilaterian ancestors. Integrating comparative evidence at the cell and organ level, we propose that the notochord evolved by modification of a ventromedian muscle followed by the assembly of an axial complex supporting swimming in vertebrate ancestors.