January American Naturalist highlights

“Frequent mating was more hazardous to females than we had suspected,” explains Priest, who conducted the study as part of his doctoral research. “Increased mating frequency actually accelerated the female aging process. But, the daughters of frequent mating mothers had enhanced offspring production.” Are the benefits to daughters enough to recoup the costs of mating" The authors evaluated their data using a model of inclusive fitness which considered the multi-generation costs and benefits of frequent mating. They found that costs to mothers were balanced by benefits to daughters such that frequency mating was neither detrimental nor beneficial. This finding indicates that cross-generational fitness effects may play an important role in evolution of mating frequency in the fruit fly and may have a more general role in life history evolution.

That this phenomenon was discovered in the fruit fly is surprising. The fruit fly is often hailed as an example of sexual conflict, in part because males and females appeared to have conflicting optimal mating frequencies. But, the work of Priest and colleagues shows that the genes which determine mating frequency in females might actually spread faster, despite direct costs to females, when their effects are considered over multiple generations. “Sexual conflict might still have an important role in the evolution of mating behavior,” states Priest. “But, clearly, we have to consider the fitness consequences of mating over more than one generation. Males and females are not in conflict with respect to mating frequency, as they both appear to benefit from frequent mating.”

"Optimal cell size for resource uptake in fluids: a new facet of resource competition"
Kohei Yoshiyama and Christopher A. Klausmeier (Michigan State University)

Ecologists generally observe a positive relationship between sizes of predators and their prey, mainly because predators need to be large to eat a larger prey. But does this positive relationship hold for sizes of bacteria and their food molecules" Using a mathematical model, scientists at Michigan State University predict the opposite, an inverse relationship between sizes of bacteria and their resource molecules. Theoretical biologists Kohei Yoshyama and Chris Klausmeier tweaked a model of bacterial growth in an aqueous medium to account for resource transport from medium to the cell surface by molecular diffusion together with biological uptake processes, and derived a negative relationship between sizes of resource molecule and bacterial cell that is most efficient in the resource competition. They also showed that two bacterial consumers can coexist on two resources that are identical except for their sizes. This result implies that size differences of resource molecules, regardless of the quality, can promote microbial diversity. “Theoretically, smaller cells are more favored under transport limitation for resource uptake than under limitations by biological processes, such as membrane uptake or catalysis within cells. As resource molecules become smaller, the molecular diffusion speeds up. And then the transport limitation for resource uptake is relaxed, and the optimal cell size becomes larger,” states Kohei Yoshiyama, the study's leading author. He adds, “Species diversity, at least at stable environments, is constrained by number of resources, which previously considered to be finite. Our results add a new dimension to the concept of 'resource', making the number of resources infinite.”