Modification of reproductive schedule in response to pathogen exposure in a wild insect: Support for the terminal investment hypothesis

In the production of the infective cercariae of trematodes, the terminal investment hypothesis of life-history theory predicts that the rate of host exploitation and cercarial production should increase during the period of cercarial shedding since the reproductive value of the parasite decreases during this period. In contrast, a bet hedging hypothesis that focuses on the success of transmission when host contact rate is variable predicts that cercarial production should decrease in an attempt to keep the host alive for longer and thus would increase the probability of successful transmission. We examined these two hypotheses under laboratory conditions and recorded the production ofDiplostomum spathaceumcercariae from naturally infected snail hosts,Lymnaea stagnalis. The average number of cercariae produced per day decreased as the snail host approached death counter to the terminal investment hypothesis. The finding supports the prediction of the bet hedging hypothesis and implies that the pattern of cercarial production may be explained by reduced virulence of the parasite within the snails to ensure extended total production time of cercariae. Nevertheless, survival of infected snails was still lower than uninfected snails suggesting that ultimately the infection still increased snail mortality rate. Cercarial production varied between days but was not cyclic, probably because of the physiology of the sporocysts within snails. Fewer cercariae were released at night, which may increase transmission efficiency to diurnally-active fish hosts. The mechanisms associated with daily cercarial production are discussed.

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Amphibians with infectious disease increase their reproductive effort: evidence for the terminal investment hypothesis

Open Biology ◽

10.1098/rsob.150251 ◽

2016 ◽

Vol 6 (6) ◽

pp. 150251 ◽

Cited By ~ 25

Author(s):

Laura A. Brannelly ◽

Rebecca Webb ◽

Lee F. Skerratt ◽

Lee Berger

Keyword(s):

Disease Resistance ◽

Reproductive Effort ◽

Batrachochytrium Dendrobatidis ◽

Population Level ◽

Life History Trait ◽

Terminal Investment ◽

Frog Species ◽

Selection For ◽

Declining Species ◽

Investment Hypothesis

Mounting an immune response to fight disease is costly for an organism and can reduce investment in another life-history trait, such as reproduction. The terminal investment hypothesis predicts that an organism will increase reproductive effort when threatened by disease. The reproductive fitness of amphibians infected with the deadly fungal pathogen Batrachochytrium dendrobatidis ( Bd ) is largely unknown. In this study, we explored gametogenesis in two endangered and susceptible frog species, Pseudophryne corroboree and Litoria verreauxii alpina. Gametogenesis, both oogenesis and spermatogenesis, increased when animals were experimentally infected with Bd . In P. corroboree , infected males have thicker germinal epithelium, and a larger proportion of spermatocytes. In L. v. alpina , infected males had more spermatic cell bundles in total, and a larger proportion of spermatozoa bundles. In female L. v. alpina , ovaries and oviducts were larger in infected animals, and there were more cells present within the ovaries. Terminal investment has consequences for the evolution of disease resistance in declining species. If infected animals are increasing reproductive efforts and producing more offspring before succumbing to disease, it is possible that population-level selection for disease resistance will be minimized.

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Older conservatives: reproduction in female Alpine chamois (Rupicapra rupicapra) is increasingly risk-averse with age

Canadian Journal of Zoology ◽

10.1139/cjz-2015-0153 ◽

2016 ◽

Vol 94 (5) ◽

pp. 311-321 ◽

Cited By ~ 12

Author(s):

A. Morin ◽

M. Rughetti ◽

S. Rioux-Paquette ◽

M. Festa-Bianchet

Keyword(s):

Reproductive Success ◽

Reproductive Effort ◽

Risk Averse ◽

Costs Of Reproduction ◽

Rupicapra Rupicapra ◽

Terminal Investment ◽

Age Dependent ◽

Alpine Chamois ◽

Old Females ◽

Investment Hypothesis

In long-lived mammals, costs of reproduction may vary with age. The terminal investment hypothesis predicts greater reproductive effort as females approach the end of their life expectancy. We monitored 97 individually marked female Alpine chamois (Rupicapra rupicapra (L., 1758)) between 2007 and 2013 to determine how age-specific reproduction affected body mass and subsequent reproductive success. We captured and weighed females between April and August and monitored reproductive success from April to October through mother–kid associations. Reproductive success was strongly age-dependent and peaked at 70% for prime-aged females (4–7 years). Reproductive senescence began at 8 years, earlier than reported by other studies of ungulates. There was no clear evidence of reproductive costs in any age class. Reproductive success was very heterogeneous for old females, suggesting variability in the onset of senescence. Old females were less likely to reproduce in poor years despite being heavier than prime-aged females, suggesting reproductive restraint in late life rather than terminal investment. Female mass remained stable from May to August with no effect of lactation. Our results suggest that chamois reproductive strategy becomes increasingly conservative with age, resulting in no detectable costs of reproduction.

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Senescent birds redouble reproductive effort when ill: confirmation of the terminal investment hypothesis

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2006.3480 ◽

2006 ◽

Vol 273 (1593) ◽

pp. 1443-1448 ◽

Cited By ~ 176

Author(s):

Alberto Velando ◽

Hugh Drummond ◽

Roxana Torres

Keyword(s):

Reproductive Success ◽

Reproductive Effort ◽

Initial Increase ◽

Male Reproductive Success ◽

Age Classes ◽

Theoretical Idea ◽

Sula Nebouxii ◽

Terminal Investment ◽

Survival And Reproduction ◽

Investment Hypothesis

This study reports an experimental confirmation of the terminal investment hypothesis, a longstanding theoretical idea that animals should increase their reproductive effort as they age and their prospects for survival and reproduction decline. Previous correlational and experimental attempts to test this hypothesis have yielded contradictory results. In the blue-footed booby, Sula nebouxii , a long-lived bird, after initial increase, male reproductive success declines progressively with age. Before laying, males of two age classes were challenged with lipopolysaccharide to elicit an immune response, which induced symptoms of declining survival prospects. Reproductive success of immune-challenged mature males fell, while that of immune-challenged old males showed a 98% increase. These results demonstrate that senescent males with poor reproductive prospects increase their effort when those prospects are threatened, whereas younger males with good reproductive prospects do not.

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