It is also a well-documented phenomenon in humans in which fertility declines dramatically during a woman's fourth decade of life (reviewed in 4). 3 In contrast, reproductive senescence has been observed in natural populations of iteroparous animals from diverse taxonomic groups including birds, mammals, reptiles, and insects (reviewed in 3).
While age-related effects on reproductive performance are hypothetically possible in semelparous species, evidence for their existence is limited. 1,2 Female reproduction is an interesting system with which to explore the process and consequences of senescence, because high and sustained fertility relies on multiple regulated processes including oogenesis, ovulation, sperm storage, fertilization, gestation (in some organisms), and oviposition/birth. Senescence is characterized as decreased physiological function over time caused by intrinsic and stochastic changes at system, organ, tissue, cell, and genetic levels. Among iteroparous animals, senescence can have large effects on female reproductive physiology and subsequent fitness. In some species, individuals experience a single reproductive episode followed by death (semelparity), while in other species individuals engage in multiple reproductive episodes during their lives (iteroparity). Understanding the genetic basis of reproductive senescence clarifies the nature of life-history trade-offs as well as potential ways to augment and/or limit female fertility in a variety of organisms.įertility is a major determinant of an animal's inclusive fitness.
Describing the processes underlying female reproductive senescence helps us understand diverse phenomena including population demographics, condition-dependent selection, sexual conflict, and transgenerational effects of maternal condition on offspring fitness. In this review, we describe how increasing maternal age in Drosophila affects reproductive fitness and offspring performance as well as the genetic foundation of these effects. The pomace fly Drosophila melanogaster is a well-established model system for exploring the physiology of reproduction and senescence. The changes in condition associated with senescence can be particularly acute for females who support reproductive processes from oogenesis through fertilization. Among animals with multiple reproductive episodes, changes in adult condition over time can have profound effects on lifetime reproductive fitness and offspring performance.
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