[Animal Behavior Alcock 10th Pdf 12
Jamar Lizarraga
John Alcock came to ASU from the University of Washington in 1972 and retired in 2008. He passed away on 1/15/2023. His research interests focus on the mating systems of insects especially those found in the Sonoran Desert. He is especially interested in how males of creatures like tarantula hawk wasps, certain beetles and the digger bee find receptive females. Now that he is retired he continues to study the mating behavior of insects on the family farm in northern Virginia. He has also written a number of books, including a textbook on animal behavior that is now in its 10th edition after having first been published in 1975.
Previous reports note that males of the Japanese bumblebee Bombus ardens ardens perform nest surveillance to mate with new queens. Here, we report that males of this species also perform patrolling and scent-marking for mating. We observed that many B. ardens ardens males fly together from May to June in circular paths through a wooded area in Tokyo, Japan. The flight activity is bimodal with peaks in the morning and late afternoon. When tethered new queens were presented at a focal point, males approached, touched, or grabbed them but ignored them at a foraging site. Males performed scent-marking on tree leaves only in the early morning (05:30 to 07:30), and compounds from the labial gland of B. ardens ardens males were detected on a scent-marked leaf. Based on these findings and previous reports, we conclude that males of this species have at least two mating tactics or strategies: nest surveillance and patrolling.
Some male animals have behavioral variations providing better mating access to females (reviewed by Alcock 2013; Gross 1996). These behavioral variations may arise from different genotypes and are recognized as alternative strategies (Shuster and Wade 1991). In other animals, they are caused by environmental factors and are referred to as alternative tactics (e.g., Thornhill 1981; Emlen 1994). In this case, the animals are considered to use a single conditioned strategy in which different tactics occur, depending on environmental factors. The conditioned strategy is typically found in animals where males fight for access to females. Since the likelihood of gaining access to females and mating may be determined by the physical ability of males, disadvantaged males may avoid direct combat and adopt alternative tactics, such as sneaking (e.g., Cook 1990) and mimicking females (e.g., Forsyth and Alcock 1990).
Bumblebee males show different premating behaviors, depending on species. At least three distinct patterns have been reported (Goulson 2003): (1) nest surveillance: males wait in front of the nest entrance and catch new queens leaving the nest, (2) perching: males form a territory and attract virgin queens with a pheromone deposited on their perch, and (3) patrolling: males fly along a circuitous path and deposit a pheromone on objects such as leaves, twigs, and rocks along the path to attract virgin queens. Males using nest surveillance and perching may engage in physical combat to defend a territory or good position for waiting for queens (Villalobos and Shelly 1987; Kindl et al. 1999). Usually, males do not fight during patrolling. Only one type of premating behavior has been reported in most bumblebee species, so the possibility of conditioned premating strategy where males use distinct mate-locating tactics depending on environmental factors has not been considered.
On the other hand, Kubo and Ono (2010) found that B. ardens ardens males produce species-specific volatiles in their labial gland (LG) with citronellol as a major compound and citronellal and citronellyl acetate as minor compounds. The secretion from LG is believed to serve as sex pheromones in the patrolling and perching strategies of other species (Kullenberg et al. 1973; Bergman and Bergstrm 1997; Kindl et al. 1999). This finding suggest that B. ardens ardens males may also use a patrolling or perching tactic in addition to nest surveillance. Males of some species which show perching strategy have distinct large compound eyes (Goulson 2003), but B. ardens ardens males are not with such a morphological character.
In 2015 and 2016, we found many B. ardens ardens males exhibiting a patrolling-like behavior in a wooded area. This study describes this behavior and discusses whether this is an alternative mate location tactic in B. ardens ardens.
If the patrolling behavior is related to mate searching, we should expect patrolling males to try to mate with queens. To examine the male response to queens, tethered queens were presented at a focal point. Three B. ardens ardens new queens were caught on flowers on 28 and 31 May 2016 and kept individually in plastic containers (dia. 9.5 cm 8 cm) with 60% sucrose solution until the experiments were carried out from 2 to 5 June 2016. Their wings were clipped to prevent absconding during the experiment. One of the three queens was hung from a branch of P. japonica at site A using fishing line (length, ca. 50 cm) tied between the thorax and abdomen. This tree had been used as a focal point by several males. The response of males flying within 50 cm of the tethered queen was classified into five categories and recorded for a 10-min observation period. The male response categories: (1) mating when male inserted their genitalia into the queen, (2) grabbing when male held the queen with their legs but did not mate, (3) contacting when touching but not grabbing the queen, (4) approaching when they turned toward the queen (
To compare the mating motivational state, the responses of males to tethered queens were also observed at a foraging site about 200 m from the study area. The same queens were tethered from a branch of a flowering Ligustrum japonicum tree (height, approx. 3 m) where many males were feeding on flowers at the same time. The behavioral responses of males were recorded for 10 min per queen as at the study site. Assays of the patrolling and foraging sites were carried out on the same day for one queen.
Volatiles were collected from the scent-marked leaf, unmarked leaf, and crushed LG by SPME headspace sampling for 20 min in the laboratory. A SPME device (Supelco Co.) with a fused-silica fiber coated with polydimethylsiloxane (PDMS, 100-μm thickness) was used.
All samples for GCMS were analyzed using a gas chromatograph-mass spectrometer (GCMS-QP2010; Shimadzu Co.) with electron ionization. The injection port had a narrow-bore (0.75-mm id) glass liner to minimize peak broadening. A DB-5MS column (60 m 0.32 mm id, 0.25-μm thickness; J&W Scientific Co.) was used to separate components. A splitless injector mode (250 C) and He carrier gas were used. The carrier flow was 1.7 mL/min, and the interface temperature was 260 C. The column temperature was held at 50 C and then increased to 250 C at 5 C/min. GCMS analysis was performed once for each sample.
The volatiles were identified based on comparison of obtained mass spectra of samples with spectra in the WILEY mass spectra library and were confirmed by chromatography with standard chemicals. The following standard chemicals were used for identification: citronellal (Tokyo Kasei Industry Co.) and citronellol (Kanto Chemical Industry Co.).
We saw eight large B. ardens ardens females that appeared to be queens in the study site during the 2-year observation period (2015 and 2016). Five flew across the male path and disappeared somewhere, and three burrowed into the soil, probably for hibernation. However, no mating with males was seen at the study site.
In 2016, the first male flight at the study site was observed on 18 May. Prior to this day, no male was found at this site, even on nearby flowers foraged intensively by B. ardens ardens workers. After 18 May, males were often observed on flowers near the study site.
The number of patrolling males changed with time of day in a similar manner at two sites A and B. Patrolling activity was high in the morning and late afternoon but declined at noon (Fig. 3). We first observed B. ardens ardens males performing scent-marking in the early morning of 25 May 2016. They landed on a leaf and walked rapidly along its edge while pressing the ventral side of the body against the leaf edge. They visited different leaves sequentially and showed the same behavior. On 10 June, we recorded the occurrence of this behavior and found that it occurred between 05:30 and 07:30 (Fig. 3b). Scent-marked plants were used as focal points later in the day. Temperature and relative humidity in the 2 days are shown in Fig. S2.
Flying males often approached a queen tethered at a focal point. Some grabbed her with their legs and pressed the tip of their abdomen against her. However, such interactions were seldom observed at a foraging site (Fig. 4), although males repeatedly entered the vicinity of a queen. Chi-squared tests showed that males responded by grabbing, contacting, or approaching to tethered queens significantly more frequently at the patrolling site than at the foraging site (queen A: χ 2 = 15.01, d.f. = 1, P
Citronellol was detected from 8 of 13 scent-marked leaves. Citronellal was also detected in one of them. Those compounds were not detected from unmarked leaves (N = 13) (Fig. 5a, b). The total ion chromatogram for the LG confirmed citronellol and citronellal as the major and minor compounds, respectively (Fig. 5c). Citronellyl acetate, another minor compound reported by Kubo and Ono (2010), was not detected in this LG sample.
Based on previous observations, B. ardens ardens males have been thought to find mates by nest surveillance. However, we found males performing circuitous flights and scent-marking of objects on the flight path. These behaviors are consistent with premating patrolling reported in other Bombus species (Kullenberg et al. 1973; Svensson 1979; Bergman and Bergstrm 1997). Furthermore, we demonstrated that males performing circuitous flights were sexually motivated by presenting them with tethered queens. Free (1971) showed that Bombus pratorum males attempted mating with tethered queens at a focal point but did not respond to queens away from focal points. Males of many Bombus species patrol actively in the morning and decrease activity in the afternoon (Svensson 1979; Bertsch 1984; Goulson 2003). However, the flight activity pattern was slightly different in B. ardens ardens which became active again in the late afternoon; other behavioral features were the same as those in patrolling males of other species. These findings clearly indicate that the observed behavior of B. ardens ardens males is premating patrolling.
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