Influence of exogenous gonadotropin-releasing hormone on seasonal reproductive behavior of the coyote (Canis latrans)

Abstract

Wild Canis species such as the coyote (C. latrans) express a suite of reproductive traits unusual among mammals, including perennial pair-bonds and paternal care of the young. Coyotes also are monestrous, and both sexes are fertile only in winter; thus, they depend upon social and physiologic synchrony for successful reproduction. To investigate the mutability of seasonal reproduction in coyotes, we attempted to evoke an out-of-season estrus in October using one of two short-acting gonadotropin-releasing hormone (GnRH) agents: (1) a GnRH analogue, deslorelin (6-D-tryptophan-9-(N-ethyl-L-prolinamide)-10-deglycinamide), 2.1mg pellet sc; or (2) gonadorelin, a GnRH (5-oxoPro-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-GlyNH(2)) porcine hypothalamic extract, 2.0 microg/kg im once daily for 3 consecutive days. A transient increase in serum concentrations of estradiol and progesterone (1 and 2 wk, respectively) was detected after treatment with deslorelin but not gonadorelin. Also, socio-sexual behaviors reminiscent of winter mating (including courtship, mate-guarding, precoital mounts, and copulatory ties) were observed among the deslorelin group. During the subsequent breeding season (January and February), however, preovulatory courtship behavior and olfactory sampling appeared suppressed; emergence of mounts and copulations were delayed in both deslorelin and gonadorelin treatment groups. Furthermore, whereas 8 of 12 females treated in October ovulated and produced healthy litters in the spring, 4 naïve coyotes failed to copulate or become pregnant. Thus, perturbation of hormones prior to ovulation in species with complex mating behaviors may disrupt critical intrapair relationships, even if fertility is not impaired physiologically.

Fig. 1

Weekly (mean ± SEM) serum estradiol concentrations (pg/mL) in female coyotes sampled after treatment with deslorelin, gonadorelin, or normal saline (October to December, 2002). Week 0 represents pretreatment baseline concentrations. Semitransparent bar represents area below the detectable limit of the RIA (<2.62 pg/mL). All gonadorelin intragroup mean estradiol concentrations were <2.6 pg/mL.

Fig. 2

Weekly (mean ± SEM) serum progesterone concentrations (ng/mL) in female coyotes sampled after treatment with deslorelin, gonadorelin, or normal saline (October to December, 2002). Standard error bars are not displayed for the gonadorelin group. Week 0 represents pretreatment baseline concentrations.

Fig. 3

Social and sexual behaviors observed among six mated coyote pairs after treatment of the females with deslorelin in October 2002. Mean steroid hormone concentrations are overlaid, demonstrating temporal relationships between behaviors and hormones.

Fig. 4

Mating behaviors observed during the coyotes’ physiologic breeding season (January to March), aligned to the estimated day of ovulation. Colony data represents 32 (untreated) coyote pairs observed during four seasons (2000–2003). Post-GnRH treatment data combines observations of four deslorelin postimplant pairs and four gonadorelin posttreatment pairs (January to February 2003). All colony and posttreatment females represented herein became pregnant.

Fig. 5

Frequency of copulatory ties observed during the coyotes’ native winter estrus, aligned to the estimated day of ovulation. Colony data represents 32 (untreated) coyote pairs observed during four breeding seasons (2000–2003). Post-GnRH treatment data combines frequency of ties observed in four deslorelin postimplant pairs and four gonadorelin posttreatment pairs (two pairs in each cohort failed to tie; January to February 2003).