Odor of Citrus trees causes sexual dimorphism in innate color preference of swallowtail butterflies
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1
The Graduate University for Advanced Studies (SOKENDAI), Department of Evolutionary Studies of Biosystems, Japan
Newly emerged pollinators searching for nectar sources exhibit innate preferences in at least two modalities: vision and olfaction. Papilio butterflies are known to be potential pollinators for reddish flowers in the field, and there is a sexual difference in innate color preference. In the olfactory modality, Papilio is attracted by the scent of citrus flowers. How these innate preferences in different modalities may interact during foraging is presently unclear. We therefore investigated the foraging behavior of naive Papilio.
We first measured the innate color preference of the Japanese yellow swallowtail butterfly, Papilio xuthus, in different ambient odor conditions. After a few days of starvation, a newly emerged Papilio was released in a small cage, where four colored disks were presented on a black floor. We identified the innate color preference by recording the color of the disk on which the starved Papilio first landed and extended its proboscis. When there was no odor in the room, more than 60% of individuals of both sexes favored blue. In the next test we introduced potted citrus trees (on which females oviposit) to the room. Surprisingly, the number of females visiting green significantly increased, at the expense of those selecting blue, but the males' behavior was unchanged. However, no such effect was elicited by potted Hibiscus (on which Papilio frequently feed). We hypothesized that citrus odor might cause this sexual dimorphism in innate color preference. Therefore, we prevented females from detecting odor by applying clear mascara to their antennae, and tested them with citrus trees present. Consistent with the hypothesis, 70% visited the blue disk.
What is neural mechanism of this sexual dimorphism? The sexual difference may exist in either the visual or the olfactory system. The Papilio compound eye contains three types of ommatidia with different combinations of spectral receptor class. We examined sexual differences in the occupancy ratio of each ommatidial type, which were determined by two anatomical properties: fluorescence under UV epi-illumination, and color of screening pigments around the rhabdom. We detected no significant difference in retinal organization between sexes. Spectral sensitivities, as measured by electroretinogram of the fronto-ventral eye, are also similar between sexes, peaking at 360nm. To explore the olfactory system, we first examined the primary olfactory processing center, the anntenal lobes (AL), using serial optical images with synapsin antibody staining. Each Papilio AL is composed of approximately 60 glomeruli. Reminiscent of the sexual difference in glomerular organization in the AL of many moths, we found at least one male-specific glomerulus in the dorsolateral AL, and three female enlarged glomeruli in the ventrolateral AL of the female. These enlarged sexual dimorphic glomeruli may relate to the behavioral phenomenon described above.
Keywords:
butterfly,
Color Vision,
innate preference,
Lepidoptera,
Olfaction
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Sensory: Vision
Citation:
Kinoshita
M,
Yoshida
M and
Arikawa
K
(2012). Odor of Citrus trees causes sexual dimorphism in innate color preference of swallowtail butterflies.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00222
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Prof. Michiyo Kinoshita, The Graduate University for Advanced Studies (SOKENDAI), Department of Evolutionary Studies of Biosystems, Hayama, Kanagawa, 240-0193, Japan, kinoshita_michiyo@soken.ac.jp