Research On The Factors Influencing Dietary Niche Expansion And The Adaptive Evolution Of Skull In Piscivorous Bats

Niche breadth change is an important process for organisms to adapt to environmental change.When the environment or characteristics of organism change,the niche often changes accordingly.Animals are often forced to abandon high-quality food resources(higher biomass or nutrition),and to choose more accessible food due to some unfavorable environmental conditions.There are also some species that have evolved from low-to high-quality food resources in nature.However,few studies have focused on the impact of food quality on niche expansion and evolution,and it is unclear what factors decide dietary niche of animal evolve from low-quality to highquality resources and how animal's phenotypes adapt to the evolution of new niche.Four species,Noctilio leporinus,Myotis vivesi,Myotis capaccinii,and Myotis pilosus,are known to regularly consume fish in the world.They have undergone expansion and evolution of the dietary niche from insects to fish.In this thesis,M.pilosus and its phylogenetically related species M.fimbriatus were used as the research object and DNA metabarcoding technique was used to analyze their diet composition,dietary niche breadth and seasonal variation to examine the effects of seasonal changes in food resources and interspecific competition on the dietary niche expansion of M.pilosus.In addition,forearm length,hindfoot length,relative hindfoot length(hindfoot/forearm)and weight of all piscivorous bats and nonfishing trawling insectivorous bats in the world were collected to test whether the morphological features of piscivorous bats have advantages over nonfishing trawling insectivorous bats.The results were the following: diet composition of M.pilosus significantly differed across seasons.Gamma dietary diversity and dietary niche breadth of the population were significantly lower in autumn than in summer,while the individual dietary diversity(alpha)was significantly lower in summer than in autumn.The dietary niche overlap between M.pilosus and M.fimbriatus in autumn was significantly higher than that of summer,and the overlap of the two species in the same season was much higher than that of a single species in different seasons.However,the proportion of fish eating in M.pilosus did not increased in autumn.The forearm length,hind foot length,relative hind foot length,and weight of M.pilosus were significantly higher than its four phylogenetically closely related trawling insectivorous bats,and the same results also found that piscivorous bats and trawlling insectivorous bats in the world.3D laser scanning combined with geometric morphometrics was used to compare the skull morphology,evolutionary rate,stretch factor and mechanical advantage of masticatory muscle between four piscivorous bats and phylogenetically related insectivorous bats to reveal how skull morphology adapts to the expansion and evolution of dietary niche.The results showed that piscivorous bats had significantly larger skulls compared with their phylogenetically related insectivorous bats.The skull shapes of Noctilio leporinus,Myotis vivesi and Myotis pilosus were obviously changed and evolutionary rate of skull size increased.Evolutionary rate of skull shape of Myotis vivesi and Myotis pilosus increased significantly.Noctilio leporinus,Myotis vivesi and Myotis pilosus have higher stretch facter of temporalis muscle and larger mechanical advantage of masseter muscle.They are suitable for producing high bite force at lower gape,but the skull of Myotis capaccinii has no higher mechanical advantage.Among the four piscivorous bats,only Myotis vivesi and Myotis pilosus have convergent shape of cranium with similar body size,and these two piscivorous bats had converged with gleaning bats.This study showed that the evolutionary force of food resources or interspecific competition may not play an important role in the evolutionary process of dietary niche expansion from low-quality resources to new high-quality resources in piscivorous bats.Instead,evolutionary potential of the organism(e.g.,foraging advantages)may be more critical.The skull of piscivorous bats changed in the direction of increasing bite force.Convergent evolution of skull shape only occurred in two piscivorous bats with similar body size,but not in all four piscivorous bats.Skull shapes are more likely to converge between species of similar size and dietary.