Natural breakage of the very long intromittent organ of the seed bug Lygaeus simulans (Heteroptera: Lygaeidae)

Abstract

Abstract. The male intromittent organ of the seed bug Lygaeus simulans ends in a long, sclerotized structure which is used to transfer sperm during mating. Observations suggest that this structure becomes brittle and is liable to breakage after being artificially exposed to the air for an extended period of time. In this study we investigate the frequency of intromittent organ breakage in L. simulans. We first examined the intromittent organ of a sample of males that mated once, and found that breakage was rare. We hypothesised that breakages are likely to be more frequent if a male is able to mate multiple times, and so we next paired males with a female for 21 days in order to provide the opportunity for multiple mating. Almost a quarter (22.5%) of these males exhibited signs of genital breakage. The point of breakage varied: for six males only the tip of the structure (around 6% of its length) was missing, whereas for three males over 50% of the structure was missing. However we were unable to locate any fragments of male genitalia in the reproductive tracts of any females that came into contact with these males. This suggests that breakages do not necessarily occur during mating itself, but instead probably occur as the intromittent organ is being retracted into the genital capsule following mating. In this species breakage may not significantly reduce male reproductive fitness as sperm transfer may still be possible.

Penetration mechanics of a beetle intromittent organ with bending stiffness gradient and a soft tip

“…Therefore, the flagellum tip is always exposed to the danger of breakage. Dougherty and Shuler ( 27 ) previously revealed such natural breakage of the flagellum-like intromittent organ in a seed bug species, Lygaeus simulans (Heteroptera: Lygaeidae), and showed that the fractures occurred mainly at the tip. In addition to the difference in material stiffness, the initially curved, softer tip would reduce the probability of being crushed between the flagellum tip and the spermathecal duct wall.…”

“…In addition, the elongated part of the intromittent organ seems to be very fragile [in an extreme case, its diameter is less than 2 μm ( 24 )]. Nevertheless, breakage of the elongated structures does not often occur [0.8 to 3.4% of males of different earwig species ( 26 ), 1.0% of single-mated seed bug males, 22.5% of multiple-mated seed bug males ( 27 ), and 4.5% of field-collected females of a leaf beetle species had within a broken piece of the male intromittent organ ( 24 )]. How do these animals achieve their challenging task without breaking their thin and seemingly fragile structures?…”