Date of Award

2026-05-01

Degree Name

Master of Science

Department

Environmental Sciences

Advisor(s)

Elizabeth J. Walsh

Abstract

As climate continues to change, weather events such as heat waves and precipitation are expected to become more extreme, and organisms living in these ephemeral habitats will experience unprecedented conditions that may test their limits. However, some organisms that live in these habitats are adapted for resiliency in the face of fluctuating conditions. The focal taxa of this study are rotifers, which have the ability to produce diapausing eggs, that are stored in sediment egg banks. Diapausing eggs will hatch once suitable conditions occur in the habitat, while the rest remain stored in the sediment. This strategy assists in the survival of a species through long periods of instability. In this study, I used rehydration experiments of temporary playa sediments to determine how increasing temperatures and changing hydroperiods affect rotifer hatching dynamics and test components of the intermediate disturbance hypothesis. Using sediments from three ephemeral playas, two experiments were conducted, one manipulating temperature when treating dry sediment prior (Aim 1), and another where dry soil was rehydrated with different volumes of media as a proxy of hydroperiod (Aim 2). In Aim 1, to test the hypotheses that species richness will be highest in intermediate temperature treatments (H1), hatching will occur earlier at higher temperatures (H2), and that community structure will have a nested pattern (H3), dry sediment was exposed to 39°C (T1), 49°C (T2), or 57°C (T3) for 5 h prior to rehydration, then rehydrated with 250 ml of media, and incubated at either 38.5°C or 25°C. These experiments resulted in a total of 29 species emerging from rehydrated sediments, with 21 species emerging from the control, 25 from T1, 21 from T2, and 22 from T3, which resulted in no significant differences in species richness among temperature treatments. When analyzing hatching phenology, it was revealed that overall, temperature treatments hatched significantly earlier than the control, dependent on species response, which implies species-specific responses of rotifer diapausing stages to changes in temperature. A nestedness analysis yielded a temperature of 26.13 (p>0.05), and a Baselga beta-partitioning test found that species diversity was driven by turnover opposed to nestedness, but with low beta diversity (ÿ=0.23). In Aim 2, the hypotheses were that species richness would be highest in intermediate water volumes (H1), community structure would follow a nested pattern (H2), based around an intermediate treatment, and hatching would occur earlier in shallower treatments (H3). Dry sediment was rehydrated with 125 ml (H1), 250 ml (H2), 500 ml (H3), and 1000 ml (H4) of media and incubated at 38.5°C. 30 species emerged in these experiments, with 19 hatching in H1, 23 in H2, 22 in H3, and 21 in H4. There was a significant increase in species richness between H1 and H3, but not between other treatments. When comparing community composition among treatments, the nestedness temperature was T=27.94 (p<0.01), and the Baselga beta-partitioning analyses found that turnover was a stronger driver of community structure than nestedness, with low beta diversity (ÿ=0.27). The results of the nestedness analysis did not support Hypothesis 3. There was no significant difference in hatching phenology (LMM: F=1.48, p>0.05). which implies diapause termination might be reliant on other hatching cues not be related to hydroperiod. Multiple experimental approaches towards the study of cues of rotifer hatching are needed to get a full understanding of rotifer population dynamics in uncertain environments.

Language

en

Provenance

Received from ProQuest

File Size

114 p.

File Format

application/pdf

Rights Holder

Brent Samuel Hogue

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