Sexual dimorphism in a trophically polymorphic cichlid fish?

Sexual dimorphism in ecologically relevant traits is ubiquitous in animals. However, other types of intraspecific phenotypic divergence, such as trophic polymorphism, are less common. Because linkage to sex should often lead to balancing selection, understanding the association between sex and phenotypic divergence could help explain why particular species show high morphological variability. To determine if sexual dimorphism could be helping to maintain ecomorphological variation in a classic case of intraspecific trophic polymorphism, we examined the association between sex and morphological divergence in the cichlid Herichthys minckleyi. Although H. minckleyi with enlarged molariform teeth on their pharyngeal jaws have been reported to more commonly be male, we did not find an association between sex and pharyngeal morphotype. Sex was associated with divergence in body size (as measured through standard length). But, sex was not associated with any of the other trophic traits examined. However, pharyngeal morphotype did show an association with gut length, gape, and tooth number. Sexual dimorphism is not playing a central role in enhancing trophic diversity within H. minckleyi. J. Morphol. 276:1448–1454, 2015. © 2015 Wiley Periodicals, Inc.     

Mechanisms of digestion in the marine herbivore, the luderick, Girella tricuspidata (Quoy and Gaimard)

The effect of feeding frequency on the mechanisms of digestion in the mucosa and contents of the gastrointestinal tract of the luderick, Girella tricuspidata (Quoy and Gaimard), was determined. Use was made of the variation in utilization frequency of Enteromorpha intestinalis by C. tricuspidata fed according to two different regimes to determine the importance of these digestive mechanisms in algal digestion.
The contents of the oesophagus and stomach of fish fed ad libitum were consistently acidic whilst those from fish deprived of food were highly variable and more alkaline. The contents of the pyloric caeca. intestine and rectum were slightly alkaline in both groups.
The number of microorganisms found in the digestive tract increased with a reduction in food availability. There was no significant cellulase activity in any of the animals tested.
Amylase and lipase were found in the pyloric caeca, intestine and rectum, but were not present in the oesophagus or stomach. Lipase activities were highly variable. Although some protease was found in the posterior portion of the gut, the majority of the activity occurred in the oesophagus and stomach.
Generally, amylase, lipase, and protease activities were unaffected by a change in the feeding regime of the fish from being fed ud libitum to being fed for a period of 24 h every 5 days. It is concluded that a reduced activity of enzymes that hydrolyse algal cell contents is not the reason for the lower utilization efficiency of food-deprived fish.
It is clear that the only difference in digestive mechanisms between fish fed ad libitum and fish fed infrequently is the variation in pH of the foregut. It is considered likely that the increased acidity of the foregut of animals fed ad Iibilum facilitates hydrolysis of the algal cell walls and allows greater utilization of algae by these fish.     

Anatomy of the stomatogastric nervous system associated with the foregut in Drosophila melanogaster and Calliphora vicina third instar larvae

The stomatogastric nervous system (SNS) associated with the foregut was studied in 3rd instar larvae of Drosophila melanogaster and Calliphora vicina (blowfly). In both species, the foregut comprises pharynx, esophagus, and proventriculus. Only in Calliphora does the esophagus form a crop. The position of nerves and neurons was investigated with neuronal tracers in both species and GFP expression in Drosophila. The SNS is nearly identical in both species. Neurons are located in the proventricular and the hypocerebral ganglion (HCG), which are connected to each other by the proventricular nerve. Motor neurons for pharyngeal muscles are located in the brain not, as in other insect groups, in the frontal ganglion. The position of the frontal ganglion is taken by a nerve junction devoid of neurons. The junction is composed of four nerves: the frontal connectives that fuse with the antennal nerves (ANs), the frontal nerve innervating the cibarial dilator muscles and the recurrent nerve that innervates the esophagus and projects to the HCG. Differences in the SNS are restricted to a crop nerve only present in Calliphora and an esophageal ganglion that only exists in Drosophila. The ganglia of the dorsal organs give rise to the ANs, which project to the brain. The extensive conformity of the SNS of both species suggests functional parallels. Future electrophysiological studies of the motor circuits in the SNS of Drosophila will profit from parallel studies of the homologous but more accessible structures in Calliphora.