Dive Into the Amazing World of Abiotic Uncover Its Amazing Definition Now

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A number of abiotic and biotic factors are known to regulate arthropod attraction, colonization, and utilization of decomposing vertebrate remains. Such information is critical when assessing arthropod evidence associated with said remains in terms of forensic relevance. Interactions are not limited to just between the resource and arthropods. There is another biotic factor that has been historically overlooked; however, with the advent of high-throughput sequencing, and other molecular techniques, the curtain has been pulled back to reveal a microscopic world that is playing a major role with regards to carrion decomposition patterns in association with arthropods. The objective of this publication is to review many of these factors and draw attention to their impact on microbial, specifically bacteria, activity associated with these remains as it is our contention that microbes serve as a primary mechanism regulating associated arthropod behavior.

Forensic entomology is the well-established field of applying insect science to aid legal investigations where arthropods are associated with living [1, 2], or deceased, people [3, 4], pets [5], wildlife [6], or even livestock [7]. Historically, forensic entomologists have been asked to determine the time of death (i.e., postmortem interval (PMI)) [8, 9] in cases involving decomposing remains. Recently, however, this activity has been called into question [10, 11] with entomologists instead determining the age of insects collected from victims, in order to estimate a time of colonization, which could differ from the actual time of death (e.g., before death due to myiasis or after death resulting in a minimum PMI).

Regardless, both analyses are built upon a foundation of assumptions regarding insect activity that might not always be completely accurate, and could, therefore, impact the validity of downstream information and inferences. For instance, presuppositions, such as assuming colonization occurred after death [1, 12], insect material collected originally from the remains in question [13], the development of datasets from one region are applicable to insect populations from other regions [14, 15, 16], or even abiotic conditions [7, 17, 18, 19, 20, 21, 22, 23] at the time of death may have influenced insect activity and subsequent colonization, are important considerations in determining the time of colonization. However, presupposed estimates of such insect attributes may not necessarily line up with the actual time of death or colonization, respectively, under all circumstances [13].

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Many factors impacting insect activity in association with decomposing human remains have been recognized previously, where differences in estimates versus actual insect colonization, development, and associated succession were coupled with factors impacting the insect(s) directly. While conditions of temperature, light, access to the remains, and precipitation do, indeed, impact the behavior of forensically-important insects [7], other determinants, such as microbial colonization and physiology associated with the remains or with the insects, are now recognized as important influences on the behavior of forensically-relevant arthropods [24, 25, 26, 27]. However, little is known of specific microbial-insect inter-kingdom engagement and the resulting impact on insect activity. More specifically, how do microbes, whether associated initially with the insect or the remains, play a role in regulating arthropod detection, attraction, and colonization of decomposing remains?

While research in this arena is still in its infancy, early data indicate bacteria associated with decomposing remains could be a major factor regulating these behaviors. In fact, those abiotic factors previously listed that are known to impact insect behavior are also factors regulating microbial activity. Therefore, such abiotic influences to bacteria likely result in a perturbation through the system impacting higher trophic levels that are leading to the often-observed shifts in arthropod behavior. However, before diving into these factors and how they might facilitate the behaviors observed by arthropods associated with decomposing remains, an understanding of ecological perspective of natural processes associated with nutrient recycling of such resources is in order.

Vertebrate remains, like all decomposing material, for the most part, represent limited resources in nature [28]. As pointed out numerously in other publications, these remains are, in most cases, unpredictable in nature, and rich in nutrients; thus, making them attractive locations for colonization, reproduction, and food sources. Consequently, animals that compete for these resources are under intense pressure to quickly locate and consume them to avoid starvation, competition [29], or failure to locate a mate [30, 31].

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Limited research exploring insect-microbe interactions as related to ecological aspects of carrion degradation has been conducted [28]. Furthermore, entomological research of carrion ecology historically focused attention on post-colonization [32, 33, 34, 35, 36]. However, two recent publications have drawn attention to the pre-colonization interval [37], or pre-appearance interval [38], as being important to understand as well. These studies indicate that factors, such as temperature, and carrion and microbe-derived odors, drive attraction and subsequent colonization, and are critical to account for the elapsed time from death to discovery [37].

Until recently, microbes associated with decomposing material were often thought of simply as facilitators or recyclers of nutrients; however, Janzen [39], in his landmark publication, discussed the various roles of microbes beyond a simple nutrient recycler. In fact, recent data demonstrate Janzen was correct in his assertion that microbes are much more—they fall into most ecological categories including, but not limited to, competitor [40, 41], mutualist [42, 43], or even predator [44].

This new paradigm gives a completely different spin to appreciating insect activity associated with decomposing remains; roles bacteria and other microbes play with regards to their ecological and forensic relevance can be applied within the context of factors driving insect attraction, colonization, and utilization. In this same context, insect activity may also have an equal or opposite effect on microbial colonization and function during decomposition processes. However, it should be noted that outside of a few laboratory studies, which will be discussed later, very little is known about the complete microbial community associated with decomposing remains, associated with the arthropod, or the microbial interactions between the two.

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Researchers are still describing microbial communities associated with decomposing remains and, in most cases, descriptions and cataloging are restricted to bacteria [45, 46, 47, 48, 49]. Who is present and how these communities differ across resources are still not fully known, which presents wonderful opportunities for exploratory research and applications in insect behavior and ecology as related to forensics. Many of the currently published forensically-relevant studies of microbial communities are predominately hypothesis driven, examining the impact of abiotic and biotic factors potentially influencing microbial composition. The purpose of this paper is to present a different perspective of the decomposition process and provide some basic understanding of some, but certainly not all, factors impacting microbial activity which, in turn, likely impacts arthropod behavior (Figure 1). Though many of these factors are known, especially to microbiologists, we hope that this paper will provide concepts of the regulation of microbe-insect interactions, in order to further guide considerations of such forensically-relevant evidence.

As with arthropods, bacterial growth and activity are influenced by ambient temperature. Microorganisms can inhabit vastly different temperature ranges, which contain a minimum, maximum, and optimal temperature for growth. Temperature is one of the most important parameters regulating the activities of microorganisms. Due to the impact of temperature on all reactions of the cell, such as changes in membrane fluidity, cellular pH, and protein integrity, to name a few (Table 1), adaptation to fluctuations in temperature is possibly the most common response researched [50, 51, 52, 53].

The intrinsic metabolic rate, and consequently the energy demand, may be inflated with increasing temperature [51, 60]. Therefore, increases in temperature with only limited nutrient availability may have a negative effect on growth due to the fact that metabolism increases, though the energy needed for these processes is not available. If, instead, food resources are well-supplied, the organisms have a surplus of energy, which can be invested in biomass growth. Under these conditions, microbial biomass would increase with temperature up to a certain point where enzymes and other cellular processes cease to function. Hence, the microbial growth response becomes more complex if resource availability varies in concert with temperature.

November 2020 Thailand Dive Cruise

Sensitivity of cells to cold stress is dependent on several factors

Limited research exploring insect-microbe interactions as related to ecological aspects of carrion degradation has been conducted [28]. Furthermore, entomological research of carrion ecology historically focused attention on post-colonization [32, 33, 34, 35, 36]. However, two recent publications have drawn attention to the pre-colonization interval [37], or pre-appearance interval [38], as being important to understand as well. These studies indicate that factors, such as temperature, and carrion and microbe-derived odors, drive attraction and subsequent colonization, and are critical to account for the elapsed time from death to discovery [37].

Until recently, microbes associated with decomposing material were often thought of simply as facilitators or recyclers of nutrients; however, Janzen [39], in his landmark publication, discussed the various roles of microbes beyond a simple nutrient recycler. In fact, recent data demonstrate Janzen was correct in his assertion that microbes are much more—they fall into most ecological categories including, but not limited to, competitor [40, 41], mutualist [42, 43], or even predator [44].

This new paradigm gives a completely different spin to appreciating insect activity associated with decomposing remains; roles bacteria and other microbes play with regards to their ecological and forensic relevance can be applied within the context of factors driving insect attraction, colonization, and utilization. In this same context, insect activity may also have an equal or opposite effect on microbial colonization and function during decomposition processes. However, it should be noted that outside of a few laboratory studies, which will be discussed later, very little is known about the complete microbial community associated with decomposing remains, associated with the arthropod, or the microbial interactions between the two.

Coral Reef Ecosystem: Structure, Food Web, And Types

Researchers are still describing microbial communities associated with decomposing remains and, in most cases, descriptions and cataloging are restricted to bacteria [45, 46, 47, 48, 49]. Who is present and how these communities differ across resources are still not fully known, which presents wonderful opportunities for exploratory research and applications in insect behavior and ecology as related to forensics. Many of the currently published forensically-relevant studies of microbial communities are predominately hypothesis driven, examining the impact of abiotic and biotic factors potentially influencing microbial composition. The purpose of this paper is to present a different perspective of the decomposition process and provide some basic understanding of some, but certainly not all, factors impacting microbial activity which, in turn, likely impacts arthropod behavior (Figure 1). Though many of these factors are known, especially to microbiologists, we hope that this paper will provide concepts of the regulation of microbe-insect interactions, in order to further guide considerations of such forensically-relevant evidence.

As with arthropods, bacterial growth and activity are influenced by ambient temperature. Microorganisms can inhabit vastly different temperature ranges, which contain a minimum, maximum, and optimal temperature for growth. Temperature is one of the most important parameters regulating the activities of microorganisms. Due to the impact of temperature on all reactions of the cell, such as changes in membrane fluidity, cellular pH, and protein integrity, to name a few (Table 1), adaptation to fluctuations in temperature is possibly the most common response researched [50, 51, 52, 53].

The intrinsic metabolic rate, and consequently the energy demand, may be inflated with increasing temperature [51, 60]. Therefore, increases in temperature with only limited nutrient availability may have a negative effect on growth due to the fact that metabolism increases, though the energy needed for these processes is not available. If, instead, food resources are well-supplied, the organisms have a surplus of energy, which can be invested in biomass growth. Under these conditions, microbial biomass would increase with temperature up to a certain point where enzymes and other cellular processes cease to function. Hence, the microbial growth response becomes more complex if resource availability varies in concert with temperature.

November 2020 Thailand Dive Cruise

Sensitivity of cells to cold stress is dependent on several factors

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