Altitudinal Variation in Digestive Tract Lengh in Feirana quadranus

Selective pressures favor variation in organ size in response to environmental changes and evolutionary process. In particular, changes in environmental temperature and rainfall at different altitudes often affect food resources, thereby mediating energy intake and allocation. The digestive tract provided a functional relationship between energy intake and allocation, of which gut morphology was associated with diet changes and food quality under different environments. Here we studied altitudinal variation in the digestive tract across four Feirana quadranus populations and tested the hypothesis that relative size of digestive tract should increase with increasing altitude. The results showed that although significant variation in length of the digestive tract was observed in females among populations, altitudinal variation in relative length of digestive tract or gut was non-significant. In addition, the digestive tract length was not correlated with temperature and precipitation across the four populations. Our findings suggest that individuals living in low-temperature and-precipitation populations at high altitudes did not display longer digestive tract than high temperature and precipitation populations at low altitudes, possibly because of small populations or sample sizes.

Ecological and Geographical Reasons for the Variation of Digestive Tract Length in Anurans

Changes of environmental conditions can shape organs size evolution in animal kingdoms. In particular, environmental changes lead to difference in food resources between different habitats, thereby affecting individual’s energy intake and allocation. The digestive theory states that animals consuming food with low contents of digestible materials should result in increasing gut length. In this study, to test the hypothesis of digestive theory, we studied ecological and geographical reasons for variation in digestive tract length among 35 species of anurans distributing in different altitude and latitude. The results showed that ecological type significantly affected digestive tract length among species, with aquatic and terrestrial species having longer digestive tract than arboreal ones. Latitude was positively correlated with digestive tract length. However, altitude, as well as monthly mean temperature and precipitation, did not correlate with digestive tract length among species. Our findings suggest that aquatic and terrestrial species might forage less digestible materials than arboreal species, thereby displaying relatively longer digestive tract than arboreal species.

The Effects of Prey Items Diversity and Digestible Materials in Stomach on Digestive Tract Length in Hylarana guentheri

Difference in environmental condition shapes variation in digestive tract length in evolutionary process.In particular,environmental difference results in variation in food resource among different habitats,and thereby affecting energy intake and energy allocation.The digestive theory predicts that animals foraging high indigestible materials of stomach contents can promote the increased gut dimensions.Here,we studied variation in digestive tract and gut length across six Hylarana guentheri populations at different altitudes and latitudes to test the prediction of the digestive theory.We found that altitude and latitude did not affect variation in relative size of digestive tract and gut among populations.We also found that relative size of digestive tract and gut did not be correlated with diversity of prey items,but negatively correlated with proportion of digestible materials.Our findings suggest that individuals foraging less digestible materials display relatively longer digestive tract than individuals foraging more digestible materials.

No Evidence for the Compensation Hypothesis in the Swelled Vent Frog(Feirana quadranus)

The compensation hypothesis predicts that if the left testis is defective e.g.due to developmental stress,the increased right testis serves a compensatory role,and thereby displaying testes asymmetry which can be a reliable indicator of male body condition.Here,to test the prediction of the compensation hypothesis,we analyzed difference in size between left testis and right testis and the relationship between testes asymmetry and male body condition in the swelled vent frog(Feirana quadranus).We found that the left testis was larger than right testis,displaying a significant directional asymmetry in testes size.Although testes mass was correlated with body condition,testes asymmetry was not correlated with body condition,which cannot provide evidence that the right testis had a compensatory function.Our findings suggest no evidence for the compensation hypothesis in this species due to lacking the compensatory function in right testis.