Rapid evolution of diet choice in an introduced population of Trinidadian guppies

Eco-evolutionary theory has brought an interest in the rapid evolution of functional traits. Among them, diet is an important determinant of ecosystem structure, affecting food web dynamics and nutrient cycling. However, it is largely unknown whether diet, or diet preference, has a hereditary basis and can evolve on contemporary timescales. Here, we study the diet preferences of Trinidadian guppies Poecilia reticulata collected from directly below an introduction site of fish transplanted from a high-predation environment into a low predation site where their densities and competition increased. Behavioural assays on F2 common garden descendants of the ancestral and derived populations showed that diet preference has rapidly evolved in the introduced population in only 12 years (approx. 36 generations). Specifically, we show that the preference for high-quality food generally found in high-predation guppies is lost in the newly derived low-predation population, who show an inertia toward the first encountered food. This result is predicted by theory stating that organisms should evolve less selective diets under higher competition. Demonstrating that diet preference can show rapid and adaptive evolution is important to our understanding of eco-evolutionary feedbacks and the role of evolution in ecosystem dynamics.

Mode of maternal provisioning in the fish genus Phalloceros: a variation on the theme of matrotrophy

The placenta is a complex organ that shows high morphological diversity. Among fish, the first vertebrates that have evolved a placenta, the family Poeciliidae exhibits very diverse modes of maternal provisioning even among congeneric species. Here, we investigated the embryonic growth curve across seven recently-described species of the highly diverse genus Phalloceros (Eigenmann, 1907). We also investigated possible intraspecific differences and whether other female characteristics affected embryo mass. We found that embryo mass decreased until around stage 20 and then increased, resulting in a 1.5 to 3-fold mass gain from fertilization to birth. Embryo mass changed non-linearly with stage of development and was affected by species identity (or locality) and female somatic dry mass. This initial loss then gain of embryonic mass during development is unique among other Poeciliidae species and was conserved across populations and species, even though size at birth can vary. Other species instead either lose mass if they lack placentas or gain mass exponentially if they have placentas. The Phalloceros mode of maternal provisioning could thus represent a different form from that seen in other species of Poeciliidae.

Bite force determination in children with primary dentition

The aim of this study was to determine the bite force with primary dentition in 30 children with normal occlusion (group I), cross bite (group II) and open bite (group III). The magnitude of the bite force was determined through a pressurized transmitter tube (pressure sensor MPX 5700 Motorola), which was connected to a converse analog/digital electronic circuit. The children bit the tube with maximum force three times successively for 5 s, with a 10 s interval among each bite, and the sign was sent directly to the computer. The highest value of the three, for each patient, was considered. Analysis of variance evaluated difference among the three groups. The means of maximum bite force were 213 17, 249 63 and 241 19 N for the groups, respectively, and there were no significant statistical differences among them (P > 0.05). The analysis of correlation showed that the weight, height and bite force presented weak positive correlation (r=0.24 and 0.23). It was concluded that in the studied groups the type of occlusion did not affect the maximum values of the bite force and body variables had a small influence in this magnitude.