Females gathered in the mating areas of the largest males and mated preferentially with them. Female selectivity probably increased the genetic representation of territorial males in the next generation. About half of the observations (21 days, 53.3 h) occurred during the mating season in the months of October-December.
The positions of each iguana in a tree were recorded with reference to one of the stations mapped in the study area (207 perches were mapped in the intensively monitored tree in Guacimos).
GUACIMOS BJ
EL FRIO MASAGUARAL
MALE HIERARCHY FORMATION.-The first event of the mating season was the gradual emergence of a male dominance hierarchy. TERRITORY FORMATION.-The year-round home ranges of the males I observed often contained several sites that would eventually become mating territories.
Post
Dec. Jan
Sep. Oct
Nov. Dec
The following year, the same male, still without the use of some of his front claws, attempted to establish a territory in another tree at the Masaguaral site. Only very minor boundary changes occurred after territory formation in both years at El Frio. At El Frio, both territories contained a few leaves of Nectandra pichurum, a preferred food that he ate occasionally during long pauses between interactions.
Territorial defense often involved regular patrolling of the mating territory, presumably to intercept intrusive males and court females (see below). In male H's territory at Guacimos, there was little change in female density after establishing a territory with the second largest male in the area (Fig. 5). However, exclusion was more severe for males, making sexual size (length) dimorphism for preferred mating areas more extreme (eg, H terr. -1.3) than for the population as a whole (1.1).
As territorial boundaries were strengthened, use of territories by females stabilized, with a high proportion of females returning to the same territory in which they spent the previous night (Figure 6). Some juvenile males that did not appear or remained in a territory during the day nevertheless often slept within another male's territory, arriving late and leaving early (Figure 7). The high number of females, combined with the exclusion of small males during midday, produced an elevated ratio of female:male territory, which I call.
Hierarchy
However, she failed to attract any females and abandoned the territory after a few days. The tree that became H's territory was heavily used by females before territories were established.
Territory 10 20
Copulation
The presence of small males reduced OSR at dawn and dusk during the copulation season (Figure 8). When their body cavities began to fill with developing eggs, they stopped eating and stayed in the tree all day (Figure 10). Occupation of territories at midday coincided with the onset of mating, but preceded the cessation of feeding by an average of 7.5 ± 4.
The study territories were selected for their leaflessness and thus females moving into these territories may have been exposed to greater solar radiation in the afternoon (cf. Beuchat, 1988). However, females in areas with heavy canopy cover were observed to follow the same pattern and remain in their territories all day. Females that remained in a mating area were subjected to fewer attempts by peripheral males.
However, as the mating season progressed, peripheral males increased the number of invasions of mating territories (see below). In Masaguaral (1982), the first observed copulation attempt was on November 19 and the first observed copulation was on November 20. In Guacimos, the territorial male acquired most of the copulations occurring during the first half of the copulation season (Figure 11).
Dusk-
Noon-
Dawn- Duski
Dawn
Noon
El Frio
Non- territory
9 receptivity
D Peripheral males
Territorial male
Dec ember
Dece m be
December
Peripheral males
Time of day
I called the latter "residents". At Guacimos, 11 females resided in the intensively monitored area for some or all of the mating season. The territorial male copulated with eight of these, all of which had been resident since the beginning or nearly the beginning of the mating season. Of these eight, one of the two largest females left the territory to become resident in an adjacent territory during the mating season.
A major difference was that five of the nine females living in the group of four study trees (two territories) in Masaguaral changed territories (but not the group) several times; one switched at least 12 times. I believe that much of the iguana's mating behavior can be traced to its arboreal folivory (Troyer, 1983). The form of male-male competition is determined by the complex three-dimensionality of the iguana's arboreal habitat and the large number of females that can reside in a single tree (more than 30 per tree in the preferred habitat).
In considering differences between the conclusions of the present study and those of Dugan (1980,1982a, 1982b; see Table 5), I believe it is parsimonious to first (1) evaluate the possibility that the differences are of interpretation rather than of fact is, and (2) look for evidence that the iguanas in both studies used the same "strategy" (Austad, 1984 found different tactical expression under slightly different conditions). Most of the differences in social behavior between the llanos and Flamenco sites can follow from the microhabitat density differences. If male status was unimportant to the females, the ratio of their behavior in each of the resistance categories would not differ between them.
MALE ROLE TERRITORIAL
This definition of "forced" copulation includes cases in which the female fights violently for a portion of the copulation time, but does not necessarily fight for the entire duration of the copulation or attempt (cf. Stamps, 1983). Note that the proposed definition is based on female behavior, not an alleged conflict of interest between the sexes. The male may be physically forcing the female to act against her interests, or he may be furthering her interests by testing the strength of various potential mates.
These possibilities are not distinguished using this definition because they are not separable based on field observations. The forced mating section includes (1) a description of forced mating contexts, (2) an analysis of variability among individuals in their participation in forced matings, (3) a discussion of ecological and evolutionary factors that may be responsible for the frequent occurrence of forced copulations in this species, and (4) a review of the relevant literature on forced copulations, particularly in relation to lizards. The latter is used to test, tentatively, the generality of the evolutionary factors I have hypothesized to drive forced mergers.
34;violent.” If a trial was resisted for a prolonged period (> - 2 0 sec) or if rapid, repetitive, or unusual physical movements were involved (eg, fast running, jumping from branch to branch while mounted, biting, etc.) the attempt was coded as “violent.” Less dramatic responses were categorized as “mild.” Of the 243 copulatory attempts clearly seen, 29 (12%) were generally passive, 22 (9%) involved mild resistance , and the rest (79%) were violently resisted. The unresisted attempts matched the behavior reported by Dugan (1982b) for territorial male copulations in Panama. The territorial male under intensive observation at Guacimos attempted to mate 43 times and succeeded (intromission). achieved) 18 times (42%, Figure 15).
PERIPHERAL
There was a highly significant relationship between success and absence of resistance in the distribution of the territorial male's copulation attempts (G = 20.1; P < 0.001), but none in peripheral male attempts (G = 1.3; P > 0.1). Male role (either territorial or peripheral) was the only variable found to explain differences in the frequency or context of forced copulations among males. These statistics imply that females selectively resisted peripheral males and the territorial male's success was influenced by the female's behavior.
Territorial males appeared to adjust their copulatory efforts, both by not mounting most females that signaled rejection and by abandoning most copulatory attempts if the female attempted to escape once mounted. CONTEXT OF FORCED COPULATIONS. Most forced copulations occurred when a peripheral male ran into a territory and mounted the first female he encountered, or when a female left a territory and was mounted by a peripheral male, usually the first one he encountered. Although location was not generally associated with success, forced copulation attempts made on the ground were rarely (3%) successful (Table 6), perhaps because female escape attempts were unaffected by the conditions.
Female resistance was not limited to the time of day or a particular season; time of day of trial (F = 1.135;. The time of success comparison is grossly confounded by the results regarding an abnormal female (see "General Mating Behavior"). There was also a correlation between the dates of cessation of feeding and first successful mating of the territorial male (Spearman r = 0.943; P = 0.0048).
CH No interference QAdjacent female
Peripheral male Territorial male
MALE ROLE
TERRITORIAL PERIPHERAL AH
Unsuccessful mountings
Successful f l copulations I—»
TERRITORIAL MALE SUCCESSES.—Four factors have been considered possible contributors to success. The percentage of resisted attempts by a territorial male and the average strength of his resistance probably mainly reflect the interest of the female. In the intensively observed area, forced copulations were the modal type of mating behavior, including 88% of attempts and more than 50% of successful copulations.
Females resisted 95% of attempts by peripheral males, but only 56% of attempts by territorial males. It is also possible that females' preference for large mates causes them to tolerate some harassment in the territories of larger males. A dominance matrix was prepared based on which animal in each dyad had the highest score in the corresponding cells of the interaction matrix.
At Guacimos, the tops of the branches hanging over the water were preferred as roosts. Numerous such territories exist, especially at the beginning of the mating season, but they are rarely used. A field study of the social structure, mating system and display behavior of the green iguana {Iguana iguana).
Female habitat choice as a determinant of the reproductive success of the territorial male marine iguana Amblyrhynchus cristatus. Extensive notes should be collected and placed at the end of the text in a notes section.
