Elsevier

Hormones and Behavior

Volume 64, Issue 2, July 2013, Pages 211-214
Hormones and Behavior

Review
The value of comparative approaches to our understanding of puberty as illustrated by investigations in birds and reptiles

https://doi.org/10.1016/j.yhbeh.2013.05.002Get rights and content

Highlights

  • Studies of the mechanisms mediating puberty are relatively rare in birds and reptiles.

  • In birds most of the work has studied puberty in the context of seasonal breeding.

  • In both reptiles and birds, modern genetic and epigenetic tools are now available.

  • Comparative studies could take advantage of species variation in puberty onset.

Abstract

This article is part of a Special Issue "Puberty and Adolescence". Studies of birds and reptiles have provided many basic insights into the neuroendocrine control of reproductive processes. This research has elucidated mechanisms regulating both early development, including sexual differentiation, and adult neuroendocrine function and behavior. However, phenomena associated with the transition into sexual maturation (puberty) have not been a focus of investigators working on species in these taxonomic classes. Research is complicated in birds and reptiles by a variety of factors, including what can be extended times to maturation, the need to reach particular body size regardless of age, and environmental conditions that can support or inhibit endocrine responses. However, careful selection of model systems, particularly those with available genetic tools, will lead to important comparative studies that can elucidate both generalizability and diversity of mechanisms regulating the onset of reproductive maturity.

Section snippets

Introduction: sexual maturation in birds and reptiles

Puberty refers to the physiological processes by which an individual attains sexual maturity and is thus able to reproduce successfully as an adult. As such, it is a key component of the general process of development. Developmental biology has a long and distinguished history of employing a wide range of species in order to understand the complex sequence of events that underlies how a zygote is transformed into an adult (Wolper and Tickle, 2010). Curiously, although all vertebrate species go

The development of sexual maturity in birds

There are approximately 10,000 extant species of birds present on earth today (Clements, 2007). Nearly 50% of these are members of the order Passeriformes (songbirds; Clements, 2007). Passeriformes typically reach sexual maturity within one year. In temperate zone species this would mean that a nestling hatched in the late spring or summer would either migrate or overwinter and then be capable of breeding the following spring. This sort of pattern or some variant (depending on when breeding

What is the pattern of sexual development in birds that mature within their first year of life?

In seasonally breeding birds, the annual cycle of reproductive and non-reproductive activity can in many species be characterized by understanding how the birds' transition among three different physiological states that are defined based on their responsiveness to seasonal variation in photoperiod (Dawson et al., 2001, Nicholls et al., 1988). Lessons learned from the annual cycle of adults are then applied to thinking about the development of a mature reproductive state in juvenile birds. This

What is the pattern of sexual development in birds that mature in substantially less time than one year?

Some avian species breed in an opportunistic manner (Hahn et al., 2008). Opportunistic in this case, refers to the fact that some critical resources are unpredictable and species that rely on them respond with a rapid increase in reproductive physiological activity when these resources become available. Species exhibiting this pattern for the organization of reproductive activity can be contrasted with seasonally breeding species that generally track highly predictable resources such as the

What is the pattern of sexual development in birds that mature after their first year of life?

In birds that mature after their first year of life the most obvious hypothesis is that they have evolved a life history strategy of delayed maturity. If this is the case they would not breed in their first year because they are just not mature enough. However, several lines of evidence indicate that this is not the case. For example, seabirds such as Albatrosses do take a long time to mature but they still reach their full body size well before they reach sexual maturity. Also, studies of

The development of sexual maturity in reptiles

Like birds, almost 10,000 species of reptiles exist; the vast majority of which are squamates (lizards and snakes). However, the literature on puberty in reptiles is extremely thin. A PubMed search of “reptile and puberty” in November 2012 produced nine articles, three that are actually on human pediatrics. Only six relate to endocrine development in non-mammalian vertebrates (two of these are not in English and therefore may be of limited accessibility). Web of Science provided four

Discussion and conclusions

Birds and reptiles represent two diverse vertebrate taxa that exhibit a range of adaptations in their strategies of reproduction. This diversity has informed the field of reproductive neuroendocrinology about many fascinating questions, including those associated with sexual differentiation and the control of seasonal breeding cycles. However, puberty has received much less attention in these taxa than in mammalian vertebrates. In birds, model species such as starlings have been developed that

Acknowledgments

The authors would like to thank BK Follett and J. Balthazart for discussion and access to unpublished data. GFB's work on seasonal breeding is supported by NINDS (R01 NS 35467). JW's research is supported by NIMH (R01 MH 096705 & R01 MH 055488) and NSF (I0S 0742833).

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