EARLY LIFE EFFECTS ON ENERGETIC DECISIONS

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are there reproductive costs to juvenile compensatory growth?

  Trajectories of litter size for female guppies who underwent compensatory (grey) and routine(black) growth during the juvenile stage.

Trajectories of litter size for female guppies who underwent compensatory (grey) and routine(black) growth during the juvenile stage.

Compensatory or “catch-up” growth may be an adaptive mechanism that buffers the growth trajectory of young organisms from deviations caused by reduced food availability. Theory generally assumes that rapid juvenile compensatory growth impacts reproduction only through its positive effects on age and size at maturation, but potential reproductive costs to juvenile compensatory growth remain virtually unexplored.

I used a food manipulation experiment to examine the reproductive consequences of compensatory growth in Trinidadian guppies (Poecilia reticulata). Compensatory growth did not affect adult growth rates, litter production rates, or investment in offspring size. However, compensatory growth had negative effects on litter size, independent of the effects of female body length, resulting in a 20% decline in offspring production. We discuss potential mechanisms behind this observed cost to reproduction.   

 


adult strategies for coping with a poor start to life

  Changes in standard length (mm) in females with high-high (HH), high-low (HL), low-high (LH), and low-low (LL) food across the juvenile and adult stages. Arrows point to mean age at maturation when the food level switch for HL (upper arrow) and LH (lower arrow) occurred.

Changes in standard length (mm) in females with high-high (HH), high-low (HL), low-high (LH), and low-low (LL) food across the juvenile and adult stages. Arrows point to mean age at maturation when the food level switch for HL (upper arrow) and LH (lower arrow) occurred.

  Reaction norms for fecundity of guppy females under low (L) and high (H) food conditions that were raised under low (black) and high (grey) food conditions.

Reaction norms for fecundity of guppy females under low (L) and high (H) food conditions that were raised under low (black) and high (grey) food conditions.

Low food availability during early growth and development can have long-term negative consequences for reproductive success. Phenotypic plasticity in adult life-history decisions may help to mitigate these potential costs, yet adult life-history responses to juvenile food conditions remain largely unexplored. I used a food manipulation experiment with female Trinidadian guppies (Poecilia reticulata) to examine age-related changes in adult life-history responses to early food conditions, whether these responses varied across different adult food conditions, and how these responses affected overall reproductive success.

Guppy females reared on low food as juveniles matured at a later age, at a smaller size, and with less energy reserves than females reared on high food as juveniles. In response to this setback, they changed their investment in growth, reproduction, and fat storage throughout the adult stage such that they were able to catch up in body size, increase their reproductive output, and restore their energy reserves to levels comparable to those of females reared on high food as juveniles.

The net effect was that adult female guppies did not merely mitigate but surprisingly were able to fully compensate for the potential long-term negative effects of poor juvenile food conditions on reproductive success.

 

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do life histories have a history?

  Adult growth as a function of food availability (a) in the present, (b) 2 months prior and (c) during the juvenile stage in Trinidadian guppies in a tributary to the Guanapo River in Trinidad, West Indies. Food availability is calculated as the summed ash free dry mass (g) of both algae and invertebrates per square metre. Shown are weighted partial residuals after accounting for female body size and all other environmental variables and their interactions.

Adult growth as a function of food availability (a) in the present, (b) 2 months prior and (c) during the juvenile stage in Trinidadian guppies in a tributary to the Guanapo River in Trinidad, West Indies. Food availability is calculated as the summed ash free dry mass (g) of both algae and invertebrates per square metre. Shown are weighted partial residuals after accounting for female body size and all other environmental variables and their interactions.

Environmental conditions in the present, more recent past, and during the juvenile stage can have significant effects on adult performance and population dynamics, but their relative importance and potential interactions remain unexplored.We examined the influence of food availability at the time of sampling, two months prior, and during the juvenile stage on adult somatic growth rates in wild Trinidadian guppies (Poecilia reticulata).

We found that food availability during both the early and later parts of an individual’s ontogeny had important consequences for adult growth strategies, but the direction of these effects differed among life stages and their magnitude, in some cases, depended on food levels experienced during other life stages. Current food levels and those two months prior to growth measurements had positive effects on adult growth rate, though food levels two months prior had a greater effect on growth than current food levels. In contrast, the effects of food availability during the juvenile stage were higher in magnitude but opposite in direction to current food levels and those two months prior to growth rate measurements. Individuals recruiting under low food levels grew faster as adults than individuals recruiting during periods of high food availability. There was also a positive interaction between food levels experienced during the juvenile stage and two months prior such that the effects of juvenile food level diminished as the food level experienced two months prior increased.

These results suggest that the similar conditions occurring at different life stages can have different effects on short- and long-term growth strategies of individuals within a population. They also demonstrate that, while juvenile conditions can have lasting effects on adult performance, the strength of that effect can be dampened by environmental conditions experienced as an adult.

A simultaneous consideration of past events in both the adult and juvenile stage may therefore improve predictions for individual- and population-level responses to environmental change.

 


Can parents help mitigate costs of early poor conditions?

Poor developmental conditions can have long-lasting negative effects on offspring phenotypes, but impacts often differ among species. Contrasting responses may reflect disparities in experimental protocols among single-species studies or inherent differences among species in their sensitivity to early conditions and/or ability to mitigate negative impacts. We used a common experimental protocol to assess and compare the role of parental care in mitigating effects of poor early conditions on offspring among four sympatric bird species in the wild. We experimentally induced low incubation temperatures and examined effects on embryonic developmental rates, hatching success, nestling growth rates, and parental responses. We examined the generality of these effects across four species that differ in their phylogenetic history, breeding ecology, and life histories. We found that cooling led to delayed hatching in all species, but carry-over effects on offspring differed among species. Parents of some but not all species increased their offspring provisioning rates in response to experimental cooling with critical benefits for offspring growth rates. Our study shows for the first time that species exhibit clear differences in the degree to which they are affected by poor early conditions. Observed differences among species demonstrate that parental care is a critical mechanism for mitigating potential negative effects on offspring and suggest that parental responses may be constrained to varying degrees by ecology and life histories.

 Copyright Thomas Martin

Copyright Thomas Martin