Negative energy balance in a male songbird, the Abert's towhee, constrains the testicular endocrine response to luteinizing hormone stimulation.
Energy deficiency can suppress reproductive function in vertebrates. As the orchestrator of reproductive function, endocrine activity of the hypothalamo-pituitary-gonadal (HPG) axis is potentially an important mechanism mediating such effects. Previous experiments in wild-caught birds found inconsistent relationships between energy deficiency and seasonal reproductive function, but these experiments focused on baseline HPG axis activity and none have investigated the responsiveness of this axis to endocrine stimulation. Here, we present data from an experiment in Abert's towhees, Melozone aberti, using gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) challenges to investigate whether energy deficiency modulates the plasma testosterone responsiveness of the HPG axis. Wild-caught birds were either ad libitum fed or energetically constrained via chronic food restriction during photoinduced reproductive development. Energy deficiency did not significantly affect the development of reproductive morphology, the baseline endocrine activity of the HPG axis, or the plasma testosterone response to GnRH challenge. Energy deficiency did, however, decrease the plasma testosterone responsiveness to LH challenge. Collectively, these observations suggest that energy deficiency has direct gonadal effects consisting of a decreased responsiveness to LH stimulation. Our study, therefore, reveals a mechanism by which energy deficiency modulates reproductive function in wild birds in the absence of detectable effects on baseline HPG axis activity.
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA Scott.Davies@asu.edu.
Scott
S
Davies
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
Sisi
S
Gao
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
Shelley
S
Valle
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
Stephanie
S
Bittner
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
Pierce
P
Hutton
The Roslin Institute, The Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Easter Bush, Midlothian EH25 9RG, UK.
Simone L
SL
Meddle
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
Pierre
P
Deviche
D000818:Animals; D005508:Food Deprivation; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D007986:Luteinizing Hormone / Q000494:pharmacology*; D008297:Male; D046109:Passeriformes / Q000502:physiology*; D017440:Photoperiod; D012098:Reproduction / Q000502:physiology; D013737:Testis / Q000187:drug effects* / Q000502:physiology; D013739:Testosterone / Q000097:blood*
D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone
Food restriction; Luteinizing hormone; Passerine; Photoperiod; Reproductive development; Testosterone