Does male gonopodial morphology affect male-female mating positioning in the livebearing fish Xenophallus umbratilis?

Xenophallus umbratilis is a freshwater livebearing fish that exhibits unique antisymmetry in the male gonopodium, which terminates in either a dextral or sinistral twist. This asymmetry in the gonopodium suggests that males might exhibit side-biased behavior when interacting with females to mate. We conducted two assays to assess the laterality of male and female mating interactions based on gonopodial morphology. We observed lateralized mating behavior in one test where males with sinistral gonopodial morphology interacted with a single female. However, we did not find lateralized mating behavior in males with dextral gonopodial morphology. We also examined male and female positioning in trials that placed a single female with five males, all with the same morphology. These trials also showed no evidence of lateralized body positioning.

Predation history has no effect on lateralized behavior in Brachyrhaphis rhabdophora.

Evolutionary biologists have grown increasingly interested in laterality, a phenomenon where bilaterally symmetrical organisms show a side bias in some trait. Lateralized behavior is particularly interesting because it is not necessarily tied to morphological asymmetry. What causes lateralized behavior remains largely unknown, although previous research in fishes suggest that fish might favor one eye over another to view potential food sources, mates, and to assess predation risk. Here we test the hypothesis that a history of predation risk predicts lateralized behavior in the livebearing fish Brachyrhaphis rhabdophora. To do this, we used a detour assay to test for eye bias when a focal fish approached various stimuli (predator, potential mate, novel object, and empty tank control). Contrary to our predictions, we found no differences in lateralized behavior between fish from populations that co-occurred with fish predators relative to those that do not co-occur with predators. In fact, we found no evidence for behavioral lateralization at all in response to any of the stimuli. We explore several possible explanations for why lateralized behavior is absent in this species, especially considering a large body of work in other livebearing fishes that shows that lateralized behavior does occur.

U.S. Army Parachute Mishap Fatalities: 2010-2015.

INTRODUCTION: Despite the large number of U.S. military members who conduct parachuting operations, its inherent safety risks, and the introduction of a new military parachute in 2010, little has been published in the last decade on U.S. military parachute fatalities.METHODS: Parachute fatality investigative records maintained by the U.S. Army Combat Readiness Center were reviewed for U.S. Army fatalities resulting from military parachuting operations from January 1, 2010, through December 31, 2015. De-identified data on cases were collected, including causes, lethal injuries, and demographic, environmental, and missional factors. A descriptive analysis was performed.RESULTS: There were 13 cases which met study inclusion criteria. Most occurred during static-line operations and were jumps from a C-17 aircraft using a T-11 parachute. The two most common assigned accident codes were "improper or abnormal exit" and "unstable or improper body position," which combined accounted for 33% of cases. Also noteworthy at 11% each were "entanglement," "parachute malfunction," and "dragged on the drop zone," and at 6% each were "static line injury," "lost or stolen air," and "drop zone hazard." In 69% of cases blunt force trauma was the cause of death.DISCUSSION: Incident factors included human actions, equipment failure, and the environment. Death from blunt force trauma upon impact with the ground as the most frequent lethal injury was expected for parachute operations. This descriptive study provides awareness to military leaders of circumstances in which fatalities occur. Future investigations should include data on the total number of jumps to provide a more comprehensive analysis of risk.Johnson ES, Gaydos SJ, Pavelites JJ, Kotwal RS, Houk JE. U.S. Army parachute mishap fatalities: 2010-2015. Aerosp Med Hum Perform. 2019; 90(7):637-642.