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Projeto Externo - de Outra Unidade da USP

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Jônatas de Jesus Florentino

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Does claw color advertise male prowess in the fiddler crab Leptuca uruguayensis?
Communicating is an important part of an animal’s life, whether to attract a mate, drive competitors away, or avoid predation. When communicating with conspecifics, animals often use behavioral or morphological signals to send the intended information from the signalers to the receivers. To copulate, males of many species broadcast their quality to any receiver willing to assess their signal (being it females or competitor males). That type of signaling is termed assessment signals: signals that inform female and male receivers how good the signaler male is as a sexual partner or competitor. Vocalizations, body size, color and movement displays are commonly used as assessment signals of male quality. Male fiddler crabs are prime examples of males using assessment signals. Males stand on the front of their burrows, waving their major claw. The size of the claw and the wave rate seem to inform receivers about the male signaler, which in turn use those signals to decide whether to interact or not with the male signaler. Thus, the major claw of the signaling males are assessment signals. Although most of the literature focuses on the waving displays of the fiddler crabs, other traits can also be used as signals during courtship or male-male competition. For instance, males of some fiddler crab species use acoustic signals when females are near them. Furthermore, the color of the male may also help males and females to detect the sexual maturity of the sender. Recently, we found that the major claws of the fiddler crab Leptuca uruguayensis also vary in the intensity of their colors, ranging from pale browns to vibrant reds. However, there are no studies indicating the variation in claw color may be used as a signal. Given that the claw is an important structure during waving signals, and that color may be broadcasted alongside claw size and wave rate, the color of the claw may also be an assessment signal used by males and females. To this date, however, we have no information on the function of the color of claw. Therefore, our objectives are to test (i) if the color of the major claw of male Leptuca uruguayensis is an assessment signal of their quality to competing males and potential mates, and (ii) if males with the most intense claw colors are the best at attracting females during courtship and intimidating competitors during male-male competition.
Evolutionary biology, animal communication, animal contests, female choice, behavioral ecology
We will collect males of Leptuca uruguayensis in the mangrove area of the Baía do Araçá (23°48'46.5"S, 45°24'30.3"W) in the city of São Sebastião from November 2020 to January 2021 (i.e., late spring through early summer). We will measure the crabs’ carapace width and major claw length with digital calipers and estimate their pinching force with a cantilever device. Then, we will pair the males according to their carapace, claw size, and their estimated pinching force. The paired males will be then placed in an enclosed arena in the mangrove to stimulate fighting. The arenas will comprise a ring with a diameter of approximately 20 cm set in the mud flat where the crabs were collected. The arenas will also have a single burrow within their area, for which the males should compete and encourage them to fight. The fights will be recorded with a camera, and each male will be identified as a winner or loser: whoever keeps the burrow will be deemed as the winner. After the fight, we will autotomize and photograph the major claws of the males to compare their colors. The photographs will be taken in RAW format with a digital camera equipped with a 100 mm Macro lens and positioned orthogonally to the claws. We will use two flashes and a diffuser to standardize the lighting conditions, and the photographs will be taken against a white background to avoid color distortion. To calibrate the photographs, which will allow us to measure and compare their colors reliably, we will use a color chart with grey standards of known reflectances in each photo. We will calibrate the photographs taken using the micaToolbox for ImageJ. The same tool will be used to measure the mean reflectance of the manus region of the autotomized claws, where our pilot studies indicate that the colors are more intense and stable over time. We will then use the mean reflectance values to compare the males between winner and losers.
For the female choice test, we will place a female and two males of similar carapace width and major claw length in another arena with a diameter of approximately 20 cm. Each male will be provided with a burrow to ensure that both males have the same overall quality. We will determine which male the female chooses by registering which male she approaches, how long she stays near each male and in which burrow she enters. After the female choice tests, we will autotomize and photograph the major claw of the males. All photos will be taken following the same procedures described above for males that fought one another. We will then use the mean reflectance values to compare the males that were chosen by the females and those which were not. Both tests will allow us to determine if the if the claw colors influence male-male fighting and female choice during courtship. Consequently, we will be able to conclude if the color of the major claw of male Leptuca uruguayensis is an assessment signal of their quality to competing males and/or potential mates.
We have been conducting since March 2020, when the idea started, and we will conclude the study by Febuary 2022. We will apply for a permission to collect and transport wild fauna from ICMBio (Chico Mendes Institute for Biodiversity Conservation) no later than August 2020. The permission will encompass the period for the entire study. Once the permission is granted, we would like to use the facilities and support provided by CEBIMar from October 2020 to March 2021 to carry out the fieldwork. In October 2020, we intend to visit the places we know contain stable populations of the fiddler crab Leptuca uruguayensis (e.g., Baía do Araçá and nearby mangroves). Once there, we will assess the environment and the population to ascertain where our tests will cause less impact. We will also do a series of pilot tests of male-male competition and female choice at these locations to evaluate and improve our methodology. After our pilots (probably from November 2020 onward), we will conduct the experiments of male-male competition and female choice while collecting and photographing the males. During this period, we intend to use CEBIMar’s facilities to take the photographs and store the material collected. We expect to have finished running the field tests and taking the photographs by March 2021. After that, we will transport all material collected to the Department of Ecology of the Institute of Biosciences of the University of São Paulo, where we will conduct further analyses and finish the project.


Uma mesa para podermos fotografar os animais.
Uma lupa e uma tomada.
Machos do caranguejo chama-maré Leptuca uruguayensis
Baía do Araçá e entorno
Maré baixa e sol
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