Differences in rectal amino acid levels determine bacteria-originated sex pheromone specificity in two closely related flies

Bactrocera dorsalis is a notorious invasive species. Along with it, its "cousin" Bactrocera cucurbitae, has a similar morphological and sexual pheromone composition. So, why they can avoid mating with their "cousins"? Amino acid, glucose,bacteria,which is the decisive factor?

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In the intricate world of nature,finding and judging a suitable mate is pivotal for reproduction in many animals. Sex pheromones are widely used by insects as a reproductive isolating mechanism to attract conspecifics and repel heterospecifics. Closely related species usually have similar sex pheromones that may only differ in the ratio of the different chemical components. However, the differentiation mechanism of sex pheromones in closely related species is still unclear.

In order to understand the mechanism, we use Bactrocera dorsalis and Bactrocera cucurbitae as the study model to investigate how the male-borne sex pheromones are different. The results demonstrated that both 2,3,5-trimethylpyrazine(TMP) and 2,3,5,6-tetramethylpyrazine (TTMP) were sex pheromones produced by rectal Bacillus using glucose and threonine (or glycine) in the two flies. However, the TMP/TTMP ratios were reversed, indicating sex pheromone specificity in the two flies (Fig 1).

在背双歧杆菌中,低 Sardh 和 ItaE 基因表达导致苏氨酸和甘氨酸合成活性降低,从而导致直肠细菌产生的 TMP/TTMP 比率较高。相反,较高的 Sardh 和 ItaE 基因表达导致较高的苏氨酸和甘氨酸合成活性,从而导致直肠细菌产生的 TMP/TTMP 比率较低。

Fig 1.Schematic illustrating the sex pheromone specificity generation hypothesis between B. dorsalis and B. cucurbitae. In B. dorsalis, low Sardh and ItaE gene expression results in lower threonine and glycine synthesis activity and thus leads to a higher TMP/TTMP ratio produced by rectal bacteria. In contrast, higher Sardh and ItaE gene expression results in higher threonine and glycine synthesis activity and thus leads to a lower TMP/TTMP ratio produced by rectal bacteria.

Through a series of experiments, we have shown that this specificity is not related to the difference in rectal Bacillus or the rectal glucose. Different amino acid levels determined the preference of rectal Bacillus to produce TMP or TTMP.

Modifications of sex pheromones are thought to represent a rapid means for altering mate recognition abilities during the evolution of new species. Our results provide insights into how interspecific sexual barriers arise. Our results may indicate a mode of evolution whereby rapid changes in chemical composition occur during speciation events, and greater divergence gradually occurs subsequently.

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Insect Hormone
Life Sciences > Biological Sciences > Physiology > Hormone > Insect Hormone
Life Sciences > Biological Sciences > Neuroscience > Behavioral Neuroscience > Sexual Behaviour > Pheromone
Life Sciences > Biological Sciences > Agriculture
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