Morphology-performance (M-P) mapping seems to be predictive of how morphology may evolve along “functional lines of least resistance”, regardless of genetic effect, but as yet it is not clear the strict (or mathematical) definition of the least functional resistance and how M-P mapping determines it. We recorded station-holding and swimming performance using a published critical swimming speed (Ucrit) test in Chinese sturgeon Acipenser sinensis, and used Ucrit as a proxy for fitness. We addressed a geometric morphometric framework to initiate Arnold’s “morphology-performance-fitness” path model (Arnold, 1983), assessing and visualizing apparent and direct M-P mapping. We quantified them as that one unit of the most-performance-covaried shape vector generated fapparent and f units of standardized performance, respectively. We defined the least functional resistance as the theoretically minimum morphological variation on an arbitrary direction in morphospace required by one unit of standardized fitness, (|b-1|min), which was calculated as a multivariate function of direct M-P mapping (f), together with the angle between paired most-performance-covaried shape vectors in morphospace (θ) and direct performance effect on fitness (w), given dual performance systems. The simulated and empirical data suggested that |b-1|min was constrained by larger sum of absolute direct effects (|fhold| + |fswim|) and absolute functional interaction (|fhold fswim cos θ|), and its direction was biased by magnitude of direct M-P mapping.

High species diversity in a community may reduce risk of infectious disease, termed the dilution effect. However, the generality of dilution effect in different disease systems remains controversial. Besides host competence, behavior of fish hosts also may play an important role in dilution or amplification of disease. Using the goldfish (Carassius auratus)-Gyrodactylus kobayashii system, effects of host competence and schooling behavior on parasite transmission were investigated while holding focal host density constant. Following competency tests of 12 fish species as potential hosts for the parasite, infection of G. kobayashii was determined on fins of goldfish mixed with each one of three different species based on their level of host competence, including the silver crucian carp, C. auratus gibelio (low competence), the grass carp, Ctenopharyngodon idellus (incompetence), the swordtail Xiphophorus helleri (incompetence), and all four species combined. Compared with mean abundance (85.8 ± 25.1) on goldfish in the control group, there was a significant decrease in the silver crucian carp group (30.0 ± 16.5), but no significant changes in the swordtail group (70.0 ± 22.2), the grass carp group (116.1 ± 33.2), or the multi-species group (75.9 ± 30.8) during the 10-day experiment. The parasite was also found on C. auratus gibelio in the silver crucian carp group and the multi-species group at a mean abundance of 7.1 and 10.9, respectively. Analysis of swimming behavior showed that the goldfish mixed well in schools with the silver crucian carp. However, the goldfish maintained separation from the grass carp and swordtail when mixed together. Distance between goldfish increased, and swimming speed and contact time decreased with the additional fish for all groups. The results suggested that the presence of a low-competence host in sufficient numbers was a necessary condition for a dilution effect due to encounter reduction, and the dilution effect may also be enhanced by changes in schooling behavior of goldfish in the presence of the low competence hosts. However, the presence of incompetent hosts did not result in any dilution effect owing to the specialist nature of the parasites and the lack of mixing with schools of goldfish.

Differences in individual personality are common amongst animals, which can play an ecological and evolutionary role given links to fitness. Personality affects animal life processes and outputs (e.g., behavior, life history, growth, survival, reproduction), and has become a common theme in animal behavioral ecology research. In the present study, we used Siberian Sturgeon to explore how personality traits of boldness and shyness are related to swimming performance, post exercise recovery and phenotypic morphology. Firstly, our results indicated that the Siberian sturgeon juveniles of shyness were better swimmers, validating evolutionary biology trade-off theory. The critical swimming speed (Ucrit) of the shy groups was higher than that of the bold groups. Secondly, the shy groups were more resilient after exercise fatigue. The swimming fatigue recovery ability, the glucose and lactic acid concentration recovery ability of shy groups were greater than that of bold groups. Thirdly, the shy groups were more streamlined. Compared with bold groups, shy groups had smaller caudate stalk lengths, caudate stalk heights, superior caudal lobes, and inferior caudal lobes. These research results further enrich the theoretical viewpoints of fish behavior biology, more importantly, which provided a good example for studying the relationship between sturgeon’s “personality” and swimming performance.