Amphioxus Behavior

Nocturnal behavior and rhythmic period gene expres... 
    "B. lanceolatum was found to be a nocturnal animal and, since its rhythmic activity persisted under constant darkness, it also appears to possess an endogenous, circadian oscillator.

    "The authors cloned a homolog of the clock gene Period (Per), which plays a central (inhibitory) role in the biochemical machinery of the circadian oscillators of both vertebrates and protostomians. This gene from B. lanceolatum was designated as amphiPer. Both the sequence of its cDNA and that of the predicted protein are more similar to those of the Per paralogs of vertebrates than to those of the single protostomian Per gene.
    A strong expression of amphiPer was found in a small cell group in the anterior neural tube. The amphiPer mRNA levels fluctuated in a rhythmic manner, being high early in the day and low late at night. The authors' data suggest a homology of the amphiPer expessing cells to the suprachiasmatic nucleus of vertebrates.

Non-synchronous spawning behavior in laboratory reared amphioxus Branchiostoma belcheri Gray
Only abstract available online.   
    "Spontaneous spawning in amphioxus (Branchiostoma belcheri Gray) was observed in a tank and the characteristics of spawning were analyzed by video recording under infrared light conditions during summer of 2001.
    Everyday when spawning was observed, without exception a male first swam up from the bottom and released sperm near the water at the surface of the tank. The initiation time of the male spawning gradually became earlier as days passed. Spawning males and females individually swam up at various intervals and released gametes. However, at the population level, the spawning pattern of amphioxus was considered to be synchronous because both males and females intensively spawned around 90 min after the spawning of the first male. The act of releasing eggs or sperms of individuals was shorter than 10 min in most of the spawning animals. "   

Insights into spawning behavior and development of the european amphioxus (Goog) 
Only abstract available online. 
It has been shown that an increase of 3–4°C in water temperature triggers spawning of the European amphioxus (Branchiostoma lanceolatum) in captivity, however, very little is known about the natural spawning behavior of this species in the field. In this work, we have followed the spawning behavior of the European amphioxus during two spawning seasons (2004 and 2005), both in the field and in captivity. We show that animals in the field spawn approximately from mid-May through early July, but depending on the year, they show different patterns of spawning. Thus, even if temperature has a critical role in the induction of the spawning in captivity, it is not the major factor in the field.

Preliminary observations on the spawning conditions of the European amphioxus (Goog) 
Only abstract available online.   
The present study found that a Mediterranean population of B. lanceolatum living near the Franco-Spanish border spawned naturally at the end of May and again at the end of June in 2003. Re-feeding experiments in the laboratory demonstrated that the gonads emptied at the end of May refilled with gametes by the end of June. We also found that animals with large gonads (both, obtained from the field and kept and fed at the laboratory during several weeks) could be induced to spawn in the laboratory out of phase with the field population if they were temperature shocked (spawning occurred 36 hours after a sustained increase in water temperature from 19°C to 25°C).

Amphioxus spawning behavior in an artificial seawater facility (Goog) 
Only abstract available online. 
    "B. lanceolatum has been chosen for this study because it is the only amphioxus species that can be induced to spawn. We provide a step-by-step guide for the assembly of such a facility and discuss the day-to-day operations required for successful animal husbandry of B. lanceolatum adults.    
    This work also includes a detailed description of the B. lanceolatum spawning behavior in captivity. Our analysis shows that the induced spawning efficiency is not sex biased, but increases as the natural spawning season progresses. We find that a minor fraction of the animals undergo phases of spontaneous spawning in the tanks and that this behavior is not affected by the treatment used to induce spawning. Moreover, the induced spawning efficiency is not discernibly correlated with spontaneous spawning in the facility.

Gonadal state of wild amphioxus populations and spawning success in...   
Adult individuals of amphioxus (Branchiostoma belcheri) were collected by dredging from a research vessel at selected stations in two areas off the coast of Japan in July 2000: Deyama and Takamatsu so named by local fishermen in the Enshu Nada Sea. The number of males collected exceeded that of females at all the stations in Takamatsu and at four of five stations in Deyama. The over all sex ratio (males : females) of the collected animals was 1.2 : 1.
    The animals showed various maturational stages of the gonad, and approximately 70% had mature gonads. However, post-spawning animals were identified only at two stations in Takamatsu. Mature animals were placed in laboratory tanks. These animals remained in good conditions for about two months, and many animals spontaneously spawned in the tanks. This is the first report of spontaneous spawning of B. belcheri in Japan."     

My speculation
    Further study suggests that swimming originally evolved as an escape behavior and was only used later by the amphioxus as a means for making its breeding more efficient. 


191211 -  1216 
180726 - 1824