Aging alters interspecific competition between two sympatric insect–parasitic nematode species

• Published in: Ecology and evolution Vol. 6; no. 11; pp. 3750 - 3759
• Main Authors: Bashey, Farrah, Sarin, Tara, Lively, Curtis M.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.06.2016; John Wiley and Sons Inc
• Subjects: Age; Age factors; Aging; Bacteria; Behavior; Breeding success; Coexistence; Competition; Competitiveness; Infections; Infectivity; Insects; Interspecific; longevity; Mortality; Nematoda; Nematodes; Niche overlap; Niches; Original Research; parasite virulence; Parasites; Physiology; Propagules; Reproduction; Seeds; Senescence; Soil testing; Species; species coexistence; Steinernema; Success; Sympatric populations; transmission stage; Viability; within‐host competition; Indiana; United States > US; Infectivity; transmission stage; Steinernema; longevity; within‐host competition; parasite virulence; species coexistence
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.2125

Interspecific competition can vary depending on the stage, age, or physiological state of the competitors. Competitive ability often increases with age or size; alternatively, senescence can lead to a loss of viability and reduced competitive success. Differences between species in their age‐specific competitive abilities can promote coexistence in the face of substantial niche overlap. We examined two sympatric species of nematodes (genus Steinernema) to determine whether their competitive relationship changes as a function of age. These obligately killing insect parasites are known for their broad host ranges and are transmitted from insect to insect via a juvenile stage propagule that is free‐living in the soil. Here, we tested whether the two species differed in the effects of age by examining the mortality of insect hosts infected with young or old transmission stage nematodes of each species. We also performed mixed infections, where an equal ratio of both species was simultaneously exposed to a host, to determine the effect of age on competitiveness. One species showed reduced performance with age, as older propagules were slower at inducing host mortality. In contrast, the other species increased in killing speed with age. In competition, insect mortality rate was predictive of competitive outcome, such that if one species induced considerably faster host death in a single‐species infection, it was competitively dominant in the coinfection. Accordingly, we found a shift in the competitive relationship between the two species with age. Our work demonstrates that species differences in the effects of aging can lead to dramatic shifts in reproductive success. As these effects are realized solely in a competitive environment, both spatial patchiness and temporal niche partitioning may be important for promoting coexistence. In this study, we examine species differences in aging in a dormant juvenile stage and the subsequent effects on interspecific competition in two insect parasitic nematode species. We find that age differentially affects infection dynamics, resulting in a shift in competitive dominance. This work supports the theoretical prediction that state‐dependent effects can facilitate species coexistence.