Sexual Behavior and Reproductive Investment in the Sapotaceae-Associated Fruit Fly Anastrepha dentata (Diptera: Tephritidae) Across Contrasting Environmental Conditions

Technical Summary: Sexual Behavior and Reproductive Investment in Anastrepha dentata

Problem and Context
The genus Anastrepha (Diptera: Tephritidae) encompasses 325 described species in the Neotropics, exhibiting diverse mating systems ranging from resource defense to lekking. While the reproductive biology of economically significant pests like Anastrepha ludens is well-documented, the biology of lesser-known, host-specialist species remains poorly understood. Specifically, species associated with the plant family Sapotaceae (e.g., Sideroxylon, Pouteria) have been hypothesized to exhibit unique reproductive traits, including delayed sexual maturation and prolonged copulation, potentially linked to host specialization. Anastrepha dentata, a fruit fly strongly associated with Sideroxylon celastrinum in Veracruz, Mexico, represents a gap in this knowledge. Prior to this study, its sexual behavior and reproductive timing were undescribed. The study aimed to characterize the mating system, courtship repertoire, and reproductive investment of A. dentata and to evaluate the consistency of these behaviors across contrasting environmental conditions (ex situ semi-natural vs. in situ natural).

Methodology
The study utilized three cohorts of A. dentata (30 males and 15 females per cohort) reared from larvae collected in infested S. celastrinum fruits in central Veracruz. Adults were maintained in mesh cages with sucrose and protein diets until sexual maturity, which preliminary observations indicated occurred 80–90 days post-emergence.

To assess behavioral plasticity, the researchers employed a crossover design observing three sequential cohorts under two distinct conditions:

1. Ex situ: Semi-natural conditions in Xalapa (temperate humid climate, 1,333 m a.s.l.) within cylindrical field cages under oak canopies.
2. In situ: Natural conditions in El Roble (warm subhumid climate, 716 m a.s.l.) within similar cages under mango canopies.

Observations were conducted over eight consecutive days per cohort (four days per site). Behavioral data were collected via focal animal sampling (10-minute intervals) and scan sampling (30-minute intervals) from 08:00 to 19:00 h. High-speed video recording (120 fps) was used to document courtship and copulation details. Environmental variables (temperature, relative humidity) were monitored at both sites. Statistical analysis utilized repeated-measures factorial ANOVA on rank-transformed data to evaluate the effects of site, time of day, and their interactions.

Key Results

• Delayed Sexual Maturation: Both sexes exhibited exceptionally delayed sexual maturation, reaching reproductive activity 80–90 days after adult emergence. This is among the longest maturation periods documented for the genus.
• Lek Dynamics and Courtship: Males formed leks of 4–16 individuals, typically on the undersides of leaves. The courtship repertoire was multimodal, involving:
  • Chemical/Visual: Swelling of pleural glands and extrusion of the proctiger.
  • Acoustic/Mechanical: Wing fanning, buzzing, and tapping.
  • Locomotor Displays: Distinctive short hopping movements (10–15 cm) between leaves, followed by "looping flights" (zigzag trajectories of 50–70 cm) accompanied by buzzing.
• Copulation Duration: Copulations were remarkably long, averaging 206.8 ± 8.6 minutes. The duration ranged from 103 to 480 minutes. Copulating pairs were rarely interrupted and often moved between perches or performed short displacement flights while attached.
• Environmental Variation: While the behavioral repertoire remained consistent across sites, the timing and frequency of specific behaviors varied.
  • Xalapa (Ex situ): Calling and abdominal movements began earlier (08:00) and were more frequent; however, fewer copulations were recorded.
  • El Roble (In situ): Looping flights and successful copulations were more frequent, particularly in the early afternoon. Copulation durations were slightly longer in El Roble (211.4 min) compared to Xalapa (195.2 min).
  • Interactions: Male-male aggressive interactions were more frequent in Xalapa, while looping flights were more frequent in El Roble.

Key Contributions
This study provides the first detailed description of the complete sexual behavior repertoire of Anastrepha dentata. It confirms that A. dentata shares the lek-based, multimodal signaling framework typical of the genus but possesses distinctive lineage-specific traits, specifically the hopping and looping displays. Furthermore, it quantifies the extreme reproductive investment in this species, characterized by the combination of delayed maturation (80–90 days) and prolonged copulation (>200 min).

Significance and Claims
The authors posit that these findings support the hypothesis that specialization on Sapotaceae hosts is associated with increased reproductive investment and unique signaling behaviors in Anastrepha. The study suggests that the delayed maturation and prolonged copulation observed in A. dentata (and similar to A. spatulata) may represent an evolutionary strategy linked to host specialization, potentially influencing mate recognition and reproductive isolation.

From a practical standpoint, the study highlights that while laboratory-based observations capture the core behavioral repertoire, environmental context significantly influences the timing and intensity of sexual activity. The authors conclude that future monitoring and management protocols (such as attract-and-kill or sterile insect technique) for A. dentata and related Sapotaceae-associated species must account for these specific temporal peaks and the species' unique behavioral plasticity. The research underscores the necessity of expanding behavioral studies beyond economically important pests to understand the full evolutionary diversity of the genus.