Effect of seawater temperature on sea urchin (Lytenchinus variegatus) gastrulation

Lydia Hull & Amanda Weihbrecht, Millersville University

 

 

 

Objective:

To test the effects of four seawater temperatures (13, 24, 27, and 30¡C) on gastrulation in sea urchin (Lytechinus variegates) embryos.

Background:

                  Sea urchins are a common indicator organism used in research, quickly showing signs of stress due to slight changes within their habitat (ÒSea Urchin EmbryologyÓ). We will use this property to assess the affect of altering the seawater temperature post-fertilization.

                  Temperature plays an important role in sea urchin development. Sea urchins of the species Lytechinus variegatus are fertile from March to October. Grown in culture, the best temperature for normal growth is around 23¡C (Mazur, 1971). This temperature would mimic the temperature embryos would be exposed to in the ocean. L. variegatus urchins can be found in the warmer areas of the Western Atlantic Ocean, ranging from North Carolina, southward toward Brazil. The species is rarely found in areas deeper than 50 meters and prefers calm, clear water (Norris, 2002).

                  Temperature is being studied, as global warming may have dire affects on the sea urchin population. The ocean temperature is not only warming, but the seawater is becoming increasingly acidic as well. In Heliocidaris erythrogamma, an increase of an additional 4¡C has been shown to decrease the occurrence of cleavage in embryos by 40 percent. Gastrulation is also affected. Normal gastrulation only occurs in four percent of the embryos with a temperature increase of 6¡C (Byrne, 2009). The ability to develop in elevated temperatures may be related to the normal environment. Species that live in more consistent environments may be less tolerant of temperature change.

Procedure:

1.     Gametes from healthy adult Lytechinus variegates were collected and fertilized following Gamete collection and Fertilization protocol.

a.     Gamete Collection

                                               i.     3 mL of 0.5 M KCl was injected to induce spawning.

                                             ii.     Using Artificial Sea Water (ASW), eggs were collected in a beaker, washed and stored at room temperature.

                                            iii.     Sperm were stored at 4 ¡C in a small test tube after collection in a dry petri dish.

b.     Fertilization Protocol

                                               i.     5 mL of eggs were allowed to settle in a test tube after being transferred from the beaker. All but 2 mL of ASW were pipetted out.

                                             ii.     Three drops of sperm were diluted in 5 mL of ASW (diluted sperm) five minutes before use because viability in water is short-term. 

                                            iii.     Diluted sperm were observed with a compound microscope to ensure motility.

                                            iv.     Eggs were fertilized with 2 drops of diluted sperm.

                                              v.     ASW was added until the tube was 90% full 5 minutes post-fertilization.

                                            vi.     A depression slide was used to view 2-3 drops of eggs 10 minutes post-fertilization.

                                           vii.     Fertilization envelopes were observed.

2.     Fertilized eggs were divided into four Petri dishes, labeled 13¡C, 24¡C, 27¡C, and 30¡C.

3.     Eggs were placed in incubators according to the temperature they were labeled. The 24¡C trial was moved to a secure location within the lab, as it developed at room temperature.

4.     As embryos developed, photos were taken throughout a 24-hour period.

Download Lab Handout

Results:

                  With normal development, the sea urchin embryos should have reached the gastrula stage within about 24 hours. Our embryos placed in the 24¡C and 27¡C environments had both reached gastrulation. The 27¡C embryos showed accelerated growth, reaching the pleuteus larva stage, in which its digestive system was completely formed before 24 hours had passed. The 24¡C embryos were slightly behind, in the late gastrula phase within 20 hours of fertilization. The embryos reared in the 30¡C and 13¡C failed to develop.

urchin 24 degrees urchin 13 degree
Text Box: Figure 1. Urchin embryos failed to develop when grown in a 13 ¡C environment. Text Box: Figure 2. Urchin embryo in late gastrulation grown at 24 ¡C, 20 hours post-fertilization.
urchin 30 degrees urchin 27 degrees
Text Box: Figure 3. Urchin embryo, 20 hours post-fertilization, in the pluteus larva stage, grown at 27 ¡C. Text Box: Figure 4. Urchin embryos grown at 30 ¡C failed to develop.

 

Discussion:

                  In this experiment, we looked at the affect of temperature on sea urchin development. From the observations made during this experiment, it can be concluded that a variation in temperature can result in death, or impaired development, of embryos. Embryos developing in 27¡C water showed accelerated development, but with just an additional increase of 3¡C, the embryos failed to develop. Without the correct temperature range in the seawater during early development, sea urchin embryos will fail to complete gastrulation. This may become an issue as global warming becomes a more prevalent issue. Species may have to adjust their habitat ranges in response to changing temperatures to find cooler areas of the ocean to grow and develop.

 

Literature Cited:  

Byrne M., Ho M., Selvakumaraswamy P., Nguyen H., Dworjanyn S., & A. Davis. Temperature, but not pH, compromises sea urchin fertilization and early development under near-future climate change scenarios. Proceedings of the Royal Society, Biological Sciences. 2009, 276:1883-1888.  

Mazure J. & J. Miller. A Description of the Complete Metamorphosis of the Sea Urchin Lytechinus variegates Cultured in Synthetic Sea Water. The Ohio Journal of Science. 1971, 71:30-36.  

Norris A, & J. Wood. ÒMarine Invertebrates of BermudaÓ. <http://www.thecephalopodpage.org/MarineInvertebrateZoology/Lytechinusvariegatus.html>.

ÒSea Urchin EmbryologyÓ. Stanford. < http://www.stanford.edu/group/Urchin/nathistory.html>.

 

 

 

© 2011 Cebra-Thomas

Last Modified: 11 May, 2011