Hirtodrosophila mycetophaga

When females visit the lek, they typically appear on the edges and stay for shorter periods of time than males do.[1] Females are also outnumbered by males. Differential access to mates has been observed in males; certain males tend to dominate the edges where females first arrive, while others are relegated to inferior positions toward the center of the lek.[1] The male closest to a newly arrived female approaches her and displays wing-scissoring behavior. In the event that other males attempt to copulate with the female, the original male will interrupt courtship to chase the other male away. These chases are usually brief and successful, with the original male being able to retain control of the female.[1]

In leks, females tend to associate with larger male aggregations.[6] The general likelihood that a fungus will be occupied increases with its surface area; larger bracket fungi have more flies.[7] However, researchers have confirmed via a multiple Poisson regression analysis that fungus area does not directly affect female distribution; male distribution is the independent variable manipulated. Females do not occupy larger bracket fungi in response to the area itself, but the fact that more males are present on them.[7]

In addition, researchers believe that the presence of optimal breeding sites or specific resources for females does not dictate where aggregations were formed.[7] Aggregations were observed in areas without resources, and fungi with ample resources were not used more often than those without resources.[7] Males were even more evenly distributed than would be expected through a random distribution. This provides evidence that males intentionally stay away from each other, and this dispersion pattern (as well as the female dispersion) provides evidence for the lek mating system.[7] It is unknown if other environmental factors may influence which specific sites H. mycetophaga utilizes.

Courtship behaviors observed in both female and male H. mycetophaga are similar to those found in other flies of the same genus.[1] Prominent wing displays are the primary similarity between the two. Both sexes move their abdomen up and down during courtship rituals, and have been observed to touch tarsi with each other. They will also sometimes attempt to use their middle and fore legs to trample the fly that they are oriented towards.[1] Additionally, both males and females extend one wing 90 degrees in displays.[1] The presence of female wing display in this species is noteworthy; previously, this had only been noted in the "lesbian" mutant phenotype of D. melanogaster.[1] Males and females both also showed waxing behavior, which entails the rapid raising and lowering of wings alternately.[1]

Males may demonstrate additional courtship behavior in the form of wing vibration and scissoring. Vibration is when the male holds his wings apart 45 degrees from one another.[1] This behavior was found during the male's approach of the female, as well as during the chasing stage. Scissoring is when the male holds his wings 90 degrees apart to form a seamless line across the body.[1] This typically lasts longer than vibration. Scissoring was more often present during circling of the female as opposed to approaching.[1] Several long bouts of scissoring are displayed to initiate copulation.[1]

Sounds accompanied the vibration and scissoring, but not wing extension. Vibration in H. mycetophaga appears as a pulse song with an inter-pulse ratio (the amount of time elapsed between pulses) of 46 ms.[1] Scissoring appears as a sine song.[1] A male tunes his aristae—the large bristle attached to the front part of the antennae—more closely with the intra-pulse frequencies of the pulse song, as opposed to the sine song.[9] The typical frequency of this call is 180 Hz, but this slows to 82 Hz as the male's wings close in preparation for copulation.[1] The sine song has been shown to increase a female's sexual activity as well as receptivity, and decreases the likelihood that she will attempt to resist the mating.[9] Moreover, the sine song was used with females that moved around less frequently, while the pulse song was employed while following or approaching females that were more active.[9]

There are other fly species that have evolved to display similar songs during different combinations of these behaviors. There are also certain similarities. D. nitidithorax has a vibration pulse song.[10] In D. enigma and D. lativittata, the wing extend is also silent.[10] Meanwhile, in D. novamaculosa, there is a bobbing pulse song and all wing movements are silent.[10] There are differences across species in the number of pulses present within one given round of a song, and the length of the inter-pulse interval also varies.[10] A key distinction between H. mycetophaga and some other fly species is that singing in H. mycetophaga occurs with both wings.[10] Use of only one wing, or even abdominal vibrations, is more commonly found.[10]

Mating success for males increases with the size of the lek along with the probability of female encounter. This relationship is linear; as size of lek increases, mating success increases proportionally.[11] However, mating success plateaus after more than 20 males gather in one lek.[11] The causal relationship between increased female encounter rate and increased mating success has not yet been established. The ideal free distribution has been tested with leks, and rejected as each male does not have an equal opportunity to mate.[11] Females prefer males in aggregations, as opposed to solitary males, and also do not choose equally within an aggregation.[11] Females are more likely to mate if the lek contains over five individuals; therefore, the optimal size for a lek is in between five and 20 males.[11]

Leks may have evolved away from the source of food because sexual displays would not be easily visible in the poorly-lit forest.[1] The fact that flies tend to aggregate only on fungi with lighter backgrounds, increasing the visibility of displays, is further evidence for this theory; visibility also accounts for the wing display behavior observed.[1] Visual stimulation seems to dominate leks, though olfactory stimulation through pheromones may be involved as well.[1]

H. mycetophaga is one of few species of Hirtodrosophila that exhibits lek mating.[11] There is a Hawaiian lekking species that is closely related, belonging to the subgenus Drosophila.[1] The presence of lekking in these related species may have resulted from convergent evolution.[1] In the Hawaiian Drosophila however, leks occur on the smooth surface of a fern leaf instead of the underside of a bracket fungus.[10]

Female-initiated models of lekking suggest that male aggregations are primarily shaped by female mate choice. On the other hand, male-initiated models suggest that female choice does not actively influence male dispersion or settlement patterns.[11] If the female-dominant model is supported, number of females (along with average male mating success) should increase with the size of the male aggregation. Meanwhile, if the male-initiated model is supported, then the distribution of males should be proportional to the number of females present.[11] However, male-initiated leks fall in line with the ideal free distribution model and the theory has therefore been rejected. Consequently, leks are more likely female-initiated.[11]

The hotspot model is one of many that have been proposed to explain lek mating. This male-initiated model suggests that male aggregations are concentrated based on areas of high female presence.[11] However, this model may not fully account for the behavior seen in H. mycetophaga.[11] Previous observations have shown that the presence of exudates (fluid emerging from the inside of an organism through some sort of opening), which would attract females, does not influence where displays occur.[11][6] Therefore, this model cannot fully account for lek mating in the species. It is possible that the distribution of certain resources may influence initial clumping.[11]

Though large aggregations of males are generally more successful, there may be costs of joining that would prevent males from joining. As group size increases, there may be increasingly antagonistic interactions between males.[11] Those males that are not dominant within the group may suffer more from these conflicts, outweighing the benefits of joining the lek. These males may be forced off of display sites.[11] Even though these males are not necessarily significantly smaller than the others, there may be other factors that make them subordinate compared to other males and unable to defend their territory such as age or previous conflict history.[11] The interference model may more accurately explain behavior in this species, as evidence of aggressive encounters within the lek has been found.[11] Poor males are forced onto smaller leks. The most competitive males are found at the best sites on the lek. These males are attractive to females because they provide genetic benefits which will be passed on to the offspring.[11]