SEASONAL DECLINES IN OFFSPRING FITNESS AND SELECTION FOR EARLY REPRODUCTION IN NYMPH-OVERWINTERING GRASSHOPPERS

Area of Science:

• Ecology
• Evolutionary Biology
• Entomology

Background:

• Phenology, or the timing of life cycle events, is crucial for species survival and reproduction.
• Nymph-overwintering grasshoppers like Arphia sulphurea and Chortophaga viridifasciata lack embryonic diapause, leading to a wide hatching range.
• Understanding the fitness consequences of varied life cycle timing is key to explaining phenological adaptations.

Purpose of the Study:

• To investigate the impact of natural and experimental variations in life cycle timing on offspring fitness.
• To identify selective pressures that shape phenology in Arphia sulphurea and Chortophaga viridifasciata.
• To determine the role of size-dependent mortality and delayed reproduction in offspring fitness.

Main Methods:

• Examined offspring fitness in Arphia sulphurea and Chortophaga viridifasciata under natural and experimental conditions.
• Utilized a cold treatment to delay hatching and extend the natural range of hatching dates.
• Assessed nymph size, overwinter mortality, and timing of reproduction in relation to hatching date.

Main Results:

• Late-hatching nymphs exhibited smaller size, increased overwinter mortality, and later reproduction compared to early-hatching nymphs.
• Size-dependent overwinter mortality strongly favors early reproduction.
• Late-maturing females compensated for delayed reproduction by reproducing faster, despite reduced adult longevity and fewer total egg pods.

Conclusions:

• Seasonal declines in offspring fitness create strong selective pressure for early reproduction in these grasshopper species.
• Female life history traits are responsive to seasonal fitness declines, demonstrating adaptive phenological adjustments.
• Experimental manipulations were essential for elucidating the fitness impacts of life-cycle timing variations.