Date of Award

2026-08-01

Degree Name

Master of Science

Department

Environmental Sciences

Advisor(s)

Elizabeth J. Walsh

Abstract

Reproduction is critical for organisms inhabiting ephemeral aquatic habitats where desiccation risk favors rapid and successful mating. Monogonont rotifers rely on sexual reproduction to produce diapausing eggs that withstand harsh conditions. I investigated how mating behaviors vary among populations of five rotifer species based on the hydroperiod of their habitat: Epiphanes brachionus and E. chihuahuaensis were sampled from habitats with short (SH) and long (LH) hydroperiods; Euchlanis dilatata was collected from a short (SH) and a permanent habitat; and Plationus patulus and Sinantherina socialis were collected from a long (LH) and a permanent (Perm) habitat. I hypothesized that SH populations would demonstrate faster, more opportunistic behaviors. To test this, I recorded 10 males and 1 female from the same population for 10 min and analyzed their behaviors. I also assessed the relationship between swimming speed and body size as well as cross-mating success. Redundancy Analysis plots (RDA) demonstrated that populations from environments with shorter hydroperiods performed reproductive behaviors more frequently and for longer periods of time than those from habitats with longer hydroperiods, likely to ensure reproductive success in time-limited environments. There were also species-specific behaviors; e.g., Epiphanes brachionus displayed novel behaviors associated with localization and copulation, not observed in other species. These included "transitioning," when the male contacts the female using his corona and foot and "copulatory spinning." The SH populations showed much greater behavioral variability in these behaviors than those collected from LH habitats. For E. chihuahuaensis, males from LH populations had higher encounter frequency and re-mated with the same female. Furthermore, geographically separated populations demonstrated emerging reproductive isolation, as seen by cross-mating failures between E. chihuahuaensis populations from SH and LH potentially indicating incipient speciation. In contrast, unexpected cross-mating occurred between two known cryptic populations in the Euchlanis dilatata complex, suggesting some degree of mating compatibility, although diapausing egg production between the pairs was rare. Additionally, females Euchlanis dilatata populations from SH displayed a 63% increase in diapausing egg production compared to permanent habitat counterparts. Morphological and swimming speed analyses showed that populations from LH or Perm waterbodies had larger overall body and corona volumes. Swimming speed varied significantly among populations from different habitat hydroperiods. Rotifers from shorter hydroperiods swam slower than populations from longer hydroperiods, except Sinantherina socialis from Perm hydroperiods which swam slower than the population from LH. This held true for adults and neonates. While laboratory experiments have limitations, my results demonstrate that rotifer mating strategies, morphology, and swimming speeds are population-specific across species and shaped by habitat predictability, suggesting adaptive flexibility in reproductive behaviors and reflecting the unique challenges and selective pressures of each habitat type.

Language

en

Provenance

Received from ProQuest

File Size

82 p.

File Format

application/pdf

Rights Holder

Ariel Bollinger

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