Animals’ mating displays are often multimodal which means that they incorporate different signaling types that include acoustic, visual, chemical, and seismic signals. Depending on environmental conditions, the males of certain species can adapt their multimodal signaling by alternating between signals. These environmental conditions can include changes in weather, rainfall, light, noise levels, and surrounding habitats. The chosen signals are advantageous and utilize the resources provided by their current environment and ignore the hindrances present. Although it is established that multimodal signaling can differ depending on environmental factors, little is known about the physiological mechanisms underlying the ability of these animals to modify their multimodal mating signals in response to changing environmental conditions.
Sex steroid hormones have an important role in controlling the various mechanisms that allow for reproduction. Changes in the environment have an impact on sex steroid and hormone production in animals. In “Mechanisms of multimodality: androgenic hormones and adaptive flexibility in multimodal displays” by Amelia R. Eigerman and Lisa A. Mangiamele, Eigerman and Mangiamele suggest that in order to fill in the gaps of our understanding of how animals have flexibility in their mating signal display, scientists should further explore the role of the endocrine system in multimodal signaling. In order to test if sex steroid hormones play a role in adaptive multimodal displays, this review utlized foot-flagging frogs (Staurois parvus) as a model organism.
Staurois parvus (Wikimedia Commons)
Foot-flagging frogs use both acoustic and visual signals in their multimodal displays that triggered by androgens (any sex steroid hormone responsible for the maintenance of male characteristics). They mate year-round and although their mating calls usually involve vocalizations, their multimodal mating display relies mainly on visual cues when there is a rise in environmental disturbance from the noise of their habitat. They often mate near streams, which may have an increase in noise levels by up to 20 dB depending on rainfall conditions. Thus, these frogs allow scientists to investigate how sex steroid hormones may play a modulating role in the adaptability of mating signals. In addition, there is preliminary data demonstrating that androgen receptors play a role in modulating the multimodal displays of male foot-flagging frogs. In fact, an abundance of androgen receptors is found in foot-flagging frogs’ hindlimbs. However, further studies will help establish that there is indeed a relationship between androgens and multimodal mating displays, especially given changing environmental conditions.
Staurois parvus has four main visual signals: foot-flagging (raising a hindlimb in a slow arc motion), foot-flashing, upright posturing, and vocal-sac inflations (with both the presence and absence of calling). A combination of these signals is usually utilized in succession during their multimodal signaling displays. In order to test whether their androgen receptors actually played a role in the modulation of their multimodal display, the researchers split the experimental group of male foot-flagging frogs into two separate groups. The first experimental group was given a single injection of 10 mg of testosterone (T) in 25 ml of 4% ethanol (which acted as a means to deliver the testosterone; VEH). The second experimental group was given 10 mg of testosterone and 50 mg of flutamide (an androgen receptor blocker that suppresses the impact of testosterone; FLUT) in 25 ml of 4% ethanol. Two males who had undergone the same injection were placed in an enclosure containing a female (to promote agonistic male-male interactions) and were recorded for a four to six hour timeframe following their injection. The researchers also played waterfall and Staurois parvus calls in the background to mimic environmental conditions. They recorded all of the behaviors displayed including contact, vocalization, visual signaling, and competition between the males.
The multimodal displays of Staurois parvus include “(a) foot-flagging, (b) foot-flashing, (c) upright posturing and (d) vocal sac inflations” (Eigerman and Mangiamele). Image e demonstrates the T + VEH and T + FLUT experimental groups.
During the laboratory experiment, the external injection of testosterone rapidly caused the foot-flagging of the frogs but did not impact their calls. This suggests that an increase in testosterone levels could be the reason why foot-flagging frogs use primarily visual signals when noise levels are too high in their habitats. As multimodal displays involve numerous signals in varying succession, it is often hard to measure shifts in signals. Thus, researchers utilized network analysis in which each network represented an individual signal in the frogs’ multimodal display. Ultimately, in both experimental groups (T + VEH and T + FLUT), the male foot-flagging frogs used visual signals primarily due to the waterfall and call noises in the background. These results are consistent with behavior observed in both wild and captive male foot-flagging frogs. However, when the androgen receptor blocker was employed, visual signals did decrease meaning they are somewhat dependent on androgens. This suggests that perhaps a more complicated, physiological system is responsible for the visual signals in the multimodal display. Another observation was that the first experimental group (T+VEH) had a greater variety of transitions between signals which may be related to the decrease of signaling repetition in the T+FLUT group. Thus, the data implies that androgens may be responsible for mediating the transitions between signals and controlling the overall multimodal display. During periods of increased rainfall, foot-flagging frogs may have a greater production of testosterone whether by physiological means or it being a seasonal occurrence.
Many animals use multimodal displays when mating. However, scientists have yet to explore the underlying physiological complexities that are responsible for these signaling patterns. Sex steroid hormones like androgens could play a crucial role in the modulation of these mating/sexual signals, especially to overcome challenges presented by their environmental conditions. This concept should be further explored especially due to the rapidly changing environmental conditions presented by the current climate crisis. With major changes to climate and weather patterns occurring, these animals will have to adapt their mating behaviors in order to continue having offspring.
Reference: Eigerman, Amelia R., and Lisa A. Mangiamele. “Mechanisms of Multimodality: Androgenic Hormones and Adaptive Flexibility in Multimodal Displays.” Animal Behaviour, Academic Press, 11 Sept. 2021, https://www.sciencedirect.com/science/article/pii/S0003347221002669.
